Behavioural Finance Glossary
Behavioural Finance Glossary
This glossary collects the core vocabulary of behavioural finance and investor psychology, defining the cognitive biases, heuristics, and decision-making patterns that shape financial markets and individual investing choices. Each term explains a concept central to understanding how real people—not perfectly rational robots—make investment decisions. Use this reference to deepen your grasp of the psychological forces that drive market cycles, portfolio construction, and trading behaviour.
Adaptive Markets Hypothesis
A market-evolution theory proposing that market efficiency varies over time as conditions change.
Rather than assuming markets are always perfectly efficient or always inefficient, the adaptive markets hypothesis suggests that market efficiency ebbs and flows. Investors adapt their strategies to changing regimes, but new conditions—such as sudden regulatory shifts or technological disruption—can trigger periods of inefficiency. This framework explains why some trading strategies work for years and then stop working once everyone knows about them.
Anchoring
The tendency to rely too heavily on an initial piece of information when making decisions.
When you see a stock at $50 that was once $100, that historical price anchors your sense of "fair value," even if new fundamentals have changed. Negotiators exploit anchoring by proposing an extreme opening number; even when rejected, it shifts the final agreement toward their desired range. In investing, anchors based on round numbers, recent highs, or a stock's listing price can distort your valuation and cause you to hold losers or pass on bargains.
Availability Heuristic
A mental shortcut that judges the likelihood of an event by how easily examples come to mind.
If news outlets heavily cover airline crashes, you may overestimate aviation risk because crash stories are vivid and memorable. Similarly, investors overweight recent market crashes or booms when assessing future risk because those examples loom large in memory. This bias causes you to overestimate the probability of events you've recently heard about, even if they're statistically rare.
Behavioural Finance
The field of study examining how psychology and cognitive biases influence financial decision-making and market outcomes.
Traditional finance assumes investors are rational and markets are efficient; behavioural finance proves they are not. It combines insights from psychology, economics, and neuroscience to explain why people consistently deviate from textbook rationality—and why those deviations are predictable enough to exploit. The discipline has grown from academic curiosity to mainstream recognition, influencing portfolio design, risk management, and regulatory policy worldwide.
Bias Blind Spot
The tendency to see yourself as less biased than others while acknowledging that biases exist.
You readily admit that anchoring and overconfidence affect most investors, yet you believe your own decisions are reasoned and objective. This meta-bias makes it harder to correct your actual biases because you don't suspect them in yourself. Even financial professionals exhibit bias blind spot, assuming their training and experience shield them from errors that ordinary investors commit.
Bounded Rationality
The idea that humans make decisions using limited information and mental resources, rather than perfect rationality.
You cannot analyze every piece of data, nor do you have unlimited time to decide whether to buy a stock. Instead, you use heuristics—mental shortcuts—to reach "good enough" decisions quickly. Bounded rationality explains why investors use rules of thumb (like "20 times earnings is fair value") and why portfolio construction often settles for simple strategies rather than mathematically optimal ones.
Bubble
A period of rapid asset-price inflation driven by investor enthusiasm and speculative buying, detached from fundamental value.
During the dot-com bubble of the late 1990s, companies with no revenue commanded billion-dollar valuations because the narrative was compelling and FOMO was rampant. Bubbles form when new asset classes (like cryptocurrencies or SPACs) generate excitement, media coverage amplifies the story, and prices rise so sharply that new buyers feel they must join before prices rise further. When sentiment reverses, prices collapse even faster than they rose.
Confirmation Bias
The tendency to search for, interpret, and remember information that confirms your existing beliefs.
If you believe a company is well-managed, you'll remember the CEO's articulate earnings calls and forget the failed product launches. You'll seek out bullish analyst reports and ignore bearish ones, or interpret negative news as a temporary setback rather than structural decline. Confirmation bias is one of the most pervasive biases in investing because it feels like open-minded research while actually narrowing your perspective.
Disposition Effect
The tendency to sell winning positions too early and hold losing positions too long.
An investor who bought at $40, sees a stock rise to $50, and quickly sells to "lock in gains" is exhibiting the disposition effect. The same investor might hold a position down to $30, hoping to break even rather than accepting the loss. This pattern arises from loss aversion and mental accounting; gains feel like house money (borrowed comfort) while losses feel painful and wrong.
Dollar-Cost Averaging
A strategy of investing a fixed amount at regular intervals, regardless of price.
An investor who puts $500 into a fund every month buys more shares when prices are low and fewer when prices are high, reducing the average cost per share over time. While dollar-cost averaging has mechanical appeal and removes the emotion of timing the market, it also means you're committing new capital even when valuation is unattractive. The strategy works best for long-term savers who have a steady income and want to remove decision-making from the equation.
Dunning-Kruger Effect
The tendency for people with low ability in a domain to overestimate their competence.
A retail trader with a few lucky wins might feel they've mastered stock picking, unaware of survivorship bias or the role of luck. Conversely, highly skilled investors often feel uncertain because they know how much they don't know. In finance, the Dunning-Kruger effect is particularly dangerous because overconfident novices take larger risks, while experienced professionals become more cautious.
Efficient Market Hypothesis
The theory that asset prices reflect all available information and cannot be beaten by active trading.
If the efficient market hypothesis were true, you could not consistently outperform the market by analyzing publicly available data because prices would already embed all known facts. The strong form claims even insider information is priced in; the weak form allows that technical analysis is futile but fundamental analysis might work. Reality shows markets are efficient enough to humiliate most active managers, yet inefficient enough that value investing and systematic strategies can generate alpha.
Endowment Effect
The tendency to value something more highly simply because you own it.
A homeowner often asks a higher price for their house than they would pay for an identical house next door. An investor holding a stock they picked personally may value it above its market price because they feel ownership pride. The endowment effect creates friction in rebalancing portfolios and makes it psychologically harder to sell inherited positions, even when selling is the rational choice.
Equity Premium Puzzle
The historical observation that stocks have outperformed bonds far more than economic theory would predict.
Standard risk models suggest stocks should beat bonds by perhaps 3–4 per cent per year to compensate for extra volatility, yet the observed premium over the past century is closer to 6–8 per cent. One explanation: investors are so loss-averse that they demand a much higher premium to accept stock volatility. Another: historical returns are inflated by survivorship bias or by extrapolating an exceptional period.
Framing Effect
The phenomenon that how a choice is presented (framed) influences your decision, even when the underlying facts are identical.
A glass half-full feels different than a glass half-empty, even though it's the same quantity of water. In investing, a fund advertised as "a 90 per cent chance of beating inflation" feels safer than one marketed as "a 10 per cent risk of falling below inflation," yet the choice is mathematically the same. Framing exploits how people process gains and losses relative to a reference point, rather than in absolute terms.
Greater Fool Theory
The investment approach of buying an overvalued asset expecting to sell it to a greater fool at an even higher price.
A trader who buys a speculative stock at inflated prices, betting that excitement will drive prices even higher, is employing greater fool theory. This strategy is profitable if you exit before the bubble pops but catastrophic if you're the last buyer. Unlike value investing, which seeks an edge in research, greater fool theory relies purely on momentum and narrative—and is vulnerable to sudden reversals of sentiment.
Herding
The tendency for investors to follow the actions of others, buying when others buy and selling when others sell.
When a stock is rising and in the news, retail investors rush to buy because others are buying, creating a self-reinforcing cycle. This herding behaviour amplifies bull markets on the way up and bear markets on the way down. Herding is rational if you assume the crowd has better information than you, but it's often irrational group psychology—the loudest voices and most visible traders attract followers regardless of merit.
Heuristic
A mental shortcut or rule of thumb that simplifies decision-making by trading accuracy for speed.
Rather than perfectly calculating a stock's value, you might use the heuristic "buy stocks trading below 15 times earnings." Heuristics work well enough in stable environments but can lead to systematic errors when conditions change. The availability heuristic, representativeness, and anchoring are all examples of how your brain trades precision for practicality.
Hindsight Bias
The tendency to see past events as more predictable than they were at the time.
After a stock crashes, you tell yourself it was obvious the company was overleveraged and the CEO was dishonest. But before the crash, those red flags were mixed with positive news and rational bullish cases. Hindsight bias makes you blame yourself for not predicting the unpredictable, and it distorts your assessment of which investment decisions were actually smart versus lucky.
House Money Effect
The tendency to take greater risks with gains than with original capital.
If you invested $10,000 and it grew to $15,000, you might take a wild speculative bet with the $5,000 gain, though you'd never risk $5,000 of your original stake the same way. Psychologically, the gain feels like found money—not really yours—so losing it stings less. The house money effect combines loss aversion with mental accounting; you're treating gains in a separate mental category where risk feels acceptable.
Illusion of Control
The tendency to overestimate your ability to control or influence outcomes that are partly or wholly dependent on chance.
A trader who believes they can time market reversals by reading charts suffers from an illusion of control; short-term price moves are largely random, not predictable. Even professional investors overestimate their ability to pick winners and time entries, leading them to make larger bets than odds would justify. This bias drives overconfidence and overleveraging.
Information Cascade
A situation where individuals ignore their private information and follow the observed actions of others.
If a stock rises sharply and well-known investors buy, subsequent investors join the rally without independent research, assuming the leaders have information they lack. Each new buyer's decision becomes public information, encouraging more buyers, until the cascade becomes self-sustaining regardless of fundamentals. Information cascades explain why trendy stocks attract crowds even when valuation is indefensible.
Investment Policy Statement
A written document outlining your investment goals, risk tolerance, asset allocation, and constraints.
An investment policy statement forces you to clarify your true risk tolerance, time horizon, and return objectives before emotions run high during a market crash. Having a written policy insulates you from panic selling and portfolio drift. It serves as an agreement with yourself: if you deviate from it, you must consciously decide to do so, rather than react to market noise.
Loss Aversion
The tendency to feel the pain of a loss roughly twice as acutely as the pleasure of an equivalent gain.
Losing $1,000 hurts more than gaining $1,000 feels good. This asymmetry, documented in prospect theory research, explains why people hold losing stocks too long (trying to avoid realizing the loss) and why bear markets cause panic selling (the pain becomes intolerable). Loss aversion shapes portfolio construction; many investors reject equity exposure because the downside terrifies them more than potential upside attracts them.
Mental Accounting
The tendency to compartmentalise financial decisions into separate mental categories, treating money differently in different "accounts."
You might be reluctant to spend $5 on a latte from cash but happily spend $5 on snacks while on holiday because you've mentally budgeted the holiday separately. In investing, you might hold a losing stock (from your "speculation account") while refusing to buy the same stock for your "safe core" portfolio. Mental accounting violates the principle that money is fungible; it allows you to hold irrational positions by keeping them in separate conceptual buckets.
Myopic Loss Aversion
The combination of loss aversion with a short time horizon, causing overreaction to short-term price volatility.
An investor checking their portfolio daily and feeling distressed by daily losses exhibits myopic loss aversion; they overweight the pain of temporary drawdowns and underweight long-term wealth creation. If the same investor checked quarterly or annually, they'd feel less distress and make fewer panic trades. This bias is exacerbated by market news cycles and mobile apps that make real-time price data too available.
Narrative Economics
The field studying how stories and narratives about the economy and markets influence investor behaviour and market outcomes.
The narrative "tech stocks always outperform" or "real estate never falls" shapes investment behaviour and can inflate prices even when fundamentals don't support it. Narrative economics recognises that humans are storytelling creatures; we make decisions based on compelling stories, not raw data. A simple narrative can spread virally through media and social networks, driving herd behaviour and bubbles.
Noise Trader
An investor who trades based on noise (rumours, hunches, short-term price movements) rather than fundamental information.
A trader who buys a stock because it's on an online forum's trending list is a noise trader. Noise traders provide liquidity and create short-term volatility, but their activity is typically random and unprofitable over time. Markets need noise traders to function, but noise trading is a wealth-transfer mechanism from noise traders to informed traders.
Overconfidence Bias
The tendency to overestimate your knowledge, skill, and ability to predict future outcomes.
Most retail traders believe they can beat the market despite evidence that 80–90 per cent of active managers underperform. Overconfidence leads to excessive trading, concentrated portfolios, inadequate diversification, and larger positions than risk management would recommend. It's particularly strong in volatile markets where short-term noise creates the illusion of predictability.
Paper Gain
An unrealised profit on a position you still own; the gain exists "on paper" but hasn't been locked in.
An investor who bought a stock at $40 and sees it at $50 has a $10 paper gain. Paper gains feel less real than realised gains (money in the bank), which leads to the disposition effect: investors happily harvest paper gains to feel successful but hold paper losses to avoid regret. The psychological reality of paper gains versus losses drives behaviour more than the mathematical reality.
Pre-mortem
A planning technique where you imagine a project or investment has already failed, then identify what went wrong.
Before making a major investment decision, imagine that the position has lost 50 per cent in the next year. What would have caused that failure—sector collapse, management fraud, missed earnings, competitive disruption? Identifying these risks in advance helps you set stop-losses, size positions appropriately, and hedge against worst-case scenarios. Pre-mortems are especially valuable because they bypass overconfidence and get you thinking like a pessimist before committing capital.
Prospect Theory
A behavioral economic theory that people evaluate choices based on relative gains and losses from a reference point, not absolute outcomes.
Prospect theory explains why people are loss-averse, why they hold losers too long, and why they sell winners too early. It formalises the value function: the pleasure of a $100 gain is smaller than the pain of a $100 loss. This groundbreaking theory by Kahneman and Tversky unified many seemingly irrational investment behaviours under a single framework.
Recency Bias
The tendency to overweight recent events and underweight older, historical information.
After a strong stock market rally, you assume the rally will continue and invest heavily, forgetting that mean reversion is common. Conversely, after a crash, you assume crashes are imminent and stay in cash, missing the early stages of recovery. Recency bias causes procyclical behaviour—buying at tops and selling at bottoms—because recent performance feels predictive even when it's mainly noise.
Reference Point
The baseline or starting point against which you mentally evaluate gains and losses.
If you bought a stock at $50, that $50 becomes your reference point; a price of $60 feels like a gain, while $40 feels like a loss, even if $40 is the stock's intrinsic value. Reference points are usually the purchase price, recent highs, or round numbers like $100. Because of loss aversion, outcomes relative to your reference point feel more important than the objective facts.
Regret Aversion
The tendency to avoid actions that might lead to regret, even when those actions are rational.
An investor might avoid selling a losing stock because they'd regret "locking in" the loss, preferring to hold in hope of recovery. Regret aversion makes action feel riskier than inaction because action brings personal responsibility for outcomes; if you do nothing and the market falls, you can blame bad luck rather than yourself. This bias leads to status quo bias and missed rebalancing opportunities.
Representativeness
The tendency to judge the likelihood of an event by how closely it matches a typical example.
If a company has excellent management, a popular product, and strong earnings growth, you might overestimate the probability that it's a good long-term investment because it "represents" the category of good companies. You ignore base rates—the fact that even good companies are often overpriced. Representativeness can lead you to chase popular stocks and high-flyer narratives rather than uncrowded value.
Risk Aversion
The preference for a certain outcome over a risky outcome with the same expected value.
Given a choice between a guaranteed $100 and a 50/50 coin flip for $200 or $0, most people choose the guarantee despite identical expected value. Risk aversion is rational when you have limited capital and ruin is possible; it becomes problematic if it leads to excessive caution and insufficient equity exposure over a long time horizon. The level of risk aversion varies widely by temperament and life circumstances.
Self-Attribution Bias
The tendency to attribute successes to your own skill and failures to external circumstances.
After a winning trade, you believe it was your superior analysis. After a losing trade, you blame market manipulation, bad luck, or a CEO's unexpected decision. Self-attribution bias boosts ego and makes you feel more competent than you are, encouraging overconfidence and larger position sizing. It also prevents genuine learning because you're not updating your beliefs about what went wrong.
Social Proof
The tendency to believe or do something because many others do, especially when uncertainty is high.
In a bull market, rising prices provide social proof that stocks are good investments, so more people buy, pushing prices higher. In a bear market, falling prices provide social proof that stocks are dangerous, so people sell, pushing prices lower. Social proof is powerful in financial markets because it's hard to assess the true value of an asset; the crowd's behaviour becomes a signal of that value.
Status Quo Bias
The tendency to prefer your current situation and resist change, even when change would be beneficial.
An investor who keeps a portfolio allocated exactly as it was ten years ago—50 per cent stocks, 50 per cent bonds—exhibits status quo bias. Life circumstances change, risk tolerance shifts, and rebalancing opportunities arise, yet inertia dominates. Status quo bias combines with loss aversion (the pain of selling a held position) and regret aversion (fear of worsening things through action) to keep portfolios stagnant.
Sunk Cost Fallacy
The tendency to continue investing time or money in a losing endeavour because of past investment, ignoring future costs and benefits.
An investor holds a stock down 50 per cent because they've already lost so much money; selling would "waste" the losses they've already suffered. But the sunk cost has no bearing on whether the stock should be held going forward. Rational decisions should ignore past costs and depend only on future expected value. The sunk cost fallacy is pervasive in investing; people hold losing stocks and underperforming funds for years because they hate admitting the past decision was wrong.
System 1 Thinking
Fast, automatic, intuitive thinking that operates with little effort and little conscious attention.
When you see a familiar stock chart, System 1 immediately tells you whether the pattern "feels" bullish or bearish without formal analysis. System 1 thinking is quick and often accurate for problems you've solved many times, but it's prone to biases and heuristics. It drives snap decisions like panic selling in a crash or euphoric buying in a rally.
System 2 Thinking
Slow, deliberate, analytical thinking that requires conscious effort and careful reasoning.
When you build a discounted cash flow model to value a company, you're using System 2 thinking. System 2 is more accurate for novel problems and complex calculations, but it's effortful, slow, and lazy—you tend to default to System 1 whenever possible. Sophisticated investing requires disciplined System 2 thinking, but emotional market moments hijack your brain and force it into System 1 mode.
Survivorship Bias
The tendency to focus on successful entities while ignoring failures, creating a distorted picture of success rates.
Historical stock market returns (roughly 10 per cent annually) reflect an index of companies that survived the entire period. Bankrupt companies are excluded, so the actual return of a random investor picking individual stocks in 1900 would be much lower. Survivorship bias affects mutual fund performance data (poorly performing funds disappear), career retrospectives (failed traders are forgotten), and any backward-looking success narrative.
Value Function
A mathematical description of how people evaluate gains and losses relative to a reference point.
The value function is steeper for losses than gains, reflecting loss aversion; it's also concave for gains (diminishing sensitivity) and convex for losses (increasing sensitivity). This function explains observed behaviour—why people hold losers (loss aversion) and why they sometimes gamble with losses to try to recover (increasing sensitivity to larger losses). The value function is central to prospect theory.
FOMO
Fear of missing out; the anxiety that others are profiting from opportunities you've passed on.
FOMO drives investors into trending stocks, cryptocurrencies, and new asset classes even when fundamental risk is high. The more viral a narrative becomes and the faster prices rise, the greater the FOMO. In social media and online forums, FOMO spreads rapidly because seeing others' gains generates envy and anxiety. FOMO-driven buying is the hallmark of late-stage bubbles.
Disposition to Rebalance
The natural inclination to restore a portfolio's original asset allocation when prices have moved it out of balance.
A portfolio split 60 per cent stocks and 40 per cent bonds will drift to 65 per cent stocks and 35 per cent bonds after a strong stock rally. The disposition to rebalance is the urge to sell some stocks and buy bonds to restore the 60/40 mix. This impulse aligns with selling winners and buying losers, which is often rational; however, rebalancing against strong trends can mean selling the best performers at exactly the wrong time.
Overtrading
The tendency to trade far more frequently than economic research justifies, driven by overconfidence and the illusion of control.
An investor checking their portfolio daily and making multiple trades per week is almost certainly overtrading. Research shows that the most active retail traders underperform the least active traders by margins that far exceed transaction costs, suggesting that overtrading is pure wealth destruction. Overtrading is driven by the illusion of control (the belief you're skillfully timing entries and exits) and noise (the mistaking of price volatility for opportunity).