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Black Monday 1987

Investor Psychology and Panic Selling

Pomegra Learn

What Were Investors Actually Thinking During the Crash?

Most accounts of Black Monday focus on the mechanical causes — portfolio insurance, program trading, specialist failures — because these are objectively documentable and causally clear. But the human dimension of the crash is at least as important: the decisions made by millions of individual and institutional investors across the trading day and the preceding weeks, the emotional states that influenced those decisions, and the narratives that shaped interpretation of events in real time. The economist Robert Shiller conducted a survey of investors in the immediate aftermath of the crash and produced one of the most detailed accounts of the psychology of a financial panic ever assembled.

Crash psychology: The pattern of emotional responses, narrative formation, and behavioral biases that leads investors to make decisions during market panics that deviate from rational expectations — including panic selling at depressed prices, herding behind the same information sources, and constructing post-hoc narratives that differ from what was actually experienced.

Key Takeaways​

  • Robert Shiller surveyed 2,000 individual investors and 1,000 institutional investors in the weeks following the crash, finding that most were acting on general anxiety and narrative rather than specific fundamental information.
  • The most commonly cited reasons for selling or concern were the market's recent declines themselves — investors were responding to prices rather than fundamentals.
  • Herd behavior was pervasive: investors were watching what other investors were doing and using that as information about what they should do.
  • Margin calls forced selling by many leveraged investors regardless of their fundamental views — mechanical, not psychological.
  • The post-crash survey revealed that "overvaluation" was widely perceived as a cause after the fact, but relatively few investors had been acting on overvaluation concerns before the crash.
  • The crash contributed significantly to the behavioral finance research program, demonstrating that investor psychology could not be treated as a second-order consideration in financial market analysis.
  • Investors who held through the crash and did not sell recovered their losses within two years; panic sellers who exited at October lows locked in permanent losses.

The Shiller Survey​

Robert Shiller, then a Yale economics professor and a pioneer in applying behavioral economics to financial markets, recognized immediately that the crash was an opportunity to study mass investor behavior with unusual richness of data. Within days of the crash, he dispatched mail surveys to approximately 2,000 individual investors and 1,000 institutional investors, asking them to describe what they had been thinking and doing during the crash and in the preceding days.

The survey responses, published in the Journal of Economic Perspectives in 1988, provided an unprecedented window into the experience of a financial panic from the participants' perspective.

The key findings were striking:

Most investors were not acting on fundamental analysis. Asked to identify the primary factor driving their trading decisions on October 19, the most common answer was the price decline itself — investors were selling because prices were falling, not because they had independently concluded that fundamental values justified selling.

Anxiety, not calculation, drove decisions. Many respondents described intense anxiety during the trading day — difficulty making decisions, emotional distress, a sense that unprecedented events were occurring. This psychological state was not conducive to careful fundamental analysis.

Narratives mattered enormously. Investors drew on historical analogies — particularly the Great Depression — to interpret what was happening. Many respondents mentioned worrying that 1929 was being repeated. This narrative frame, once adopted, implied catastrophic further declines and encouraged selling regardless of current valuation levels.

Information cascades dominated. Many investors reported watching TV coverage, calling their brokers for information, and most importantly, observing what other investors were doing. The primary information source for many was the declining prices themselves — interpreted as evidence that other, better-informed investors were selling.

Information Cascades and Herd Behavior​

The Shiller survey findings are consistent with the theoretical framework of information cascades developed by economists Abhijit Banerjee and Sushil Bikhchandani in subsequent years. An information cascade occurs when rational individuals, observing others' actions, rationally decide to follow the crowd even if their own private information suggests a different course.

The logic works as follows: Investor A observes that many investors are selling. He infers that they must have information he does not have — why else would they sell? Even if A's own analysis suggests holding, the observed selling of many others is evidence that his analysis might be wrong. Rationally updating his beliefs based on this evidence, A may decide to sell — adding another observation for investor B to follow.

In a market crash, this mechanism can generate cascading selling that has little connection to changes in fundamental value. Each seller creates evidence for the next seller that selling is justified. The cascade is self-confirming: prices fall as selling occurs, and falling prices are taken as confirmation that the sellers had good reasons.

The mechanism is not irrational at the individual level — updating beliefs based on others' revealed preferences is a reasonable way to process information in a complex environment. But at the aggregate level, it can generate large, correlated movements in prices that are driven by cascade dynamics rather than fundamental news.

The Role of Margin Calls​

One important dimension of selling behavior during the crash was not psychological at all: margin calls forced selling by leveraged investors regardless of their fundamental views. An investor who had purchased stocks on margin — using borrowed money — faced automatic sell orders when the equity in their account fell below the minimum requirement.

On October 19, with prices falling sharply from the opening, margin calls began immediately. For investors with leveraged positions, this was not a choice: either they deposited more cash (impossible for many on the speed required) or their positions were liquidated. Brokerage firms automatically sold positions to meet margin requirements, creating additional selling pressure in an already stressed market.

Margin calls are a pro-cyclical mechanism — they require selling exactly when prices are falling and buying exactly when prices are rising, amplifying rather than damping price moves. This dynamic is not unique to 1987; margin calls amplified selling in 1929, 2000, 2008, and 2020. The leveraged investor community's forced selling on October 19 was mechanical, not psychological, but its contribution to the cascade was real.

Loss Aversion and Prospect Theory​

Behavioral economists Kahneman and Tversky's prospect theory — developed in 1979 — provides a framework for understanding why investors make the choices they do during crashes. The key insight is loss aversion: losses are psychologically more painful than equivalent gains are pleasurable. An investor who has experienced a 20 percent loss feels about twice as much pain as they felt pleasure from an equivalent gain.

Loss aversion creates several behavioral patterns during market declines:

The disposition effect in reverse. Normally, investors are reluctant to realize losses (the disposition effect) — they hold losing positions hoping for recovery. But during rapid, severe declines, a different dynamic can emerge: the accelerating loss becomes psychologically intolerable, and investors sell to "stop the pain" regardless of whether selling at the current price makes fundamental sense.

Reference point anchoring. Investors compare current prices to their purchase price or recent peaks. A stock that was $50 last month and is now $40 feels like a 20 percent loss, regardless of whether $40 is actually a reasonable price. This anchoring can drive selling based on reference to past prices rather than current fundamental value.

Overweighting of recent experience. The availability heuristic — giving more weight to easily recalled events — causes investors who have just experienced a severe crash to overweight the probability of further severe declines. This compounds loss aversion: not only does the past loss feel painful, but the fear of more losses like it becomes exaggerated.

The Recovery and Regret​

Investors who sold on October 19 or in the immediately following days generally locked in permanent losses — the market recovered through 1988 and beyond. The Dow Jones Industrial Average, which had closed at 1,738 on October 19, returned to above 2,000 by January 1988 and above 2,200 by May 1988. By mid-1989, the market had exceeded its August 1987 peak.

Investors who held through the crash — either by design or by inability to act (their brokers were unreachable, or they simply could not bring themselves to sell) — experienced temporary paper losses that were completely reversed within two years.

This pattern — rapid recovery after a severe crash with no fundamental economic damage — is the scenario that makes panic selling most regrettable in retrospect. The investors who most needed to sell (those with specific cash needs, those who could not bear the volatility psychologically, those with leveraged positions that required selling) incurred the losses. Those who held recovered.

The regret of those who sold at the bottom, and the vindication of those who held, shaped investor psychology for years afterward — contributing to the "buy the dip" mentality that characterized investor behavior during subsequent market declines and arguably sustained elevated equity valuations through the 1990s and 2000s.

Common Mistakes in Analyzing Investor Behavior​

Describing panic selling as irrational. Given the information available in real time — no guarantee that the market would recover quickly, genuine uncertainty about whether the crash signaled deeper economic problems, active comparisons to 1929 — selling was not obviously irrational for every investor. For those with specific liquidity needs, high leverage, or low risk tolerance, selling was the appropriate response. The mistake was in allowing the cascade to drive decisions that were not appropriate to one's individual circumstances.

Assuming all crash buying was heroic contrarianism. Some investors who bought during the crash did so deliberately, based on valuation analysis. Others simply could not act — phone lines were jammed, and orders placed with brokers went unexecuted. "Holding through the crash" is not always the same as "choosing to hold through the crash."

Frequently Asked Questions​

Did any investors actually profit from Black Monday? Yes. Investors who had sold short equity positions before the crash — betting that prices would fall — profited. Investors who had purchased put options profited. Some hedge fund managers who had reduced equity exposure or had short positions in the preceding weeks reported significant gains.

Were institutional investors more rational than individual investors? Shiller's survey found that institutional investors were not notably more rational than individuals during the crash. They used the same information sources, made the same kinds of narrative inferences, and experienced significant anxiety. The key difference was that portfolio insurance programs at institutions executed mechanically, without the anxiety that a human decision-maker would have felt.

Why didn't investors study valuation data and conclude prices were attractive? Some did — the corporate buyback activity and the behavior of some value investors demonstrated that certain market participants were making exactly this assessment. For most investors, the pace of the decline, the communication system failures, and the psychological dynamics of the cascade made careful valuation analysis extremely difficult in real time.

Summary​

The human psychology of Black Monday — the cascade selling, the narrative formation around 1929 comparisons, the loss aversion and information cascade dynamics documented by Robert Shiller's post-crash survey — reveals that market crashes are not purely mechanical events. They are events in which millions of human beings, operating under extreme uncertainty and psychological stress, make decisions whose aggregate produces outcomes that none would have chosen individually. Understanding the psychology of crashes does not eliminate the risk of future panics, but it illuminates why they occur and what distinguishes investors whose behavior produces good outcomes (holding through or buying during panic) from those whose behavior produces permanent losses (selling at the bottom). The core insight is ancient but consistently forgotten: prices at the depth of a panic are the product of cascading fear, not of careful fundamental analysis, and the recovery to rational valuations is the norm when the underlying economy is sound.

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