The Sunk Cost Fallacy in Losing Stocks
The Sunk Cost Fallacy in Losing Stocks
You bought a stock at $80. It's now trading at $50. You're down $30 per share, or $3,000 on a 100-share position. Every instinct screams to hold until it "gets back to $80 so I can break even." This instinct is the sunk cost fallacy, and it's among the most expensive behavioral errors in investing. The price you paid is irrelevant. What matters is whether the stock will be worth more than $50 in the future.
Quick definition: The sunk cost fallacy is the mistake of making decisions based on money already spent (sunk costs) rather than on current facts and future prospects. In investing, it's holding a losing position because you want to "break even" rather than cut losses.
Key takeaways
- The original purchase price has zero influence on whether a stock should be held or sold today
- Anchoring to cost basis causes investors to hold losers far longer than fundamentals justify
- The disposition effect (holding losers, selling winners) is partially driven by sunk cost thinking
- A stock worth $50 today will either go to $60 or $40 based on future prospects, not on the fact that you paid $80
- Breaking even should not be a portfolio goal; maximizing future wealth is
- Cutting losses when the thesis breaks is not "giving up." It's adapting to new information.
The economic principle
In economics, sunk costs are irrelevant. You can't un-spend money. The only decision that matters is: given your current situation, what action maximizes future wealth?
You own a stock worth $50. The thesis has weakened: the company's growth is slowing, and a competitor has taken market share. You estimate a 30% chance it recovers to $80 (your purchase price) and a 70% chance it falls to $25. The expected value is $42.50, which is below the current price of $50. By holding, you're accepting an expected loss of $7.50 per share.
Rationally, you should sell and redeploy the $50 to a stock with better odds. But emotionally, you resist because you want to "recover" your original $80 investment. That original $80 is sunk. It doesn't change the math.
Why anchoring to cost basis feels right
The brain uses anchors—reference points—to make decisions. Your cost basis ($80) becomes the anchor. Anything above $80 is a win. Anything below is a loss. Psychologically, losses feel twice as bad as equivalent gains, so the brain locks onto the anchor and refuses to move.
Studies show that when portfolio losses are labeled on the same screen as purchase prices, investors hold longer. When losses are shown without cost basis, they're more likely to sell. The information is identical, but the framing changes behavior.
The cost of holding sunk-cost positions
Suppose you're holding three positions:
- Position A: Bought at $100, now at $50. You're holding because "it's down half; it will recover."
- Position B: Bought at $100, now at $150. You're holding because it's a winner.
- Position C: Bought at $100, now at $110. You're holding because it's slightly up.
Unknown to you, each position has a 50% probability of reaching $200 and 50% probability of reaching $25 over the next three years. Based on future prospects (not past prices), they're identical. But your behavior differs dramatically:
You sell B (lock in gains), hold A (hoping to break even), and hold C (default). Over three years, A and C face the same odds, but because you anchored to cost basis, you manage them differently.
If A falls to $20, you feel like you "cut your losses" (emotionally accurate but financially wrong—you should have sold at $50). If B rises to $250, you've exited early (and feel regret, even though selling was a sunk-cost correction).
Real-world scenario: The $10,000 mistake
You invested $100,000 across 10 positions ($10,000 each) in January 2022. By March 2022:
- 3 positions are down 50% to $5,000 each
- 4 positions are flat to slightly down (off by $500–$1,000 each)
- 3 positions are up 15% to $11,500 each
Total portfolio: ~$92,000 (down 8%).
You're tempted to "cut losses" on the down 50% positions to "protect the rest." But the real question is: do those three positions have the highest expected returns going forward, or the lowest? If they've fallen because the entire market fell (bear market), and they still have good fundamentals, selling them is a sunk-cost mistake. If they've fallen because the business deteriorated, selling is right—but not because you want to break even.
Distinguishing sunk-cost errors from good stops
A good sell decision: "The thesis broke. The company's market share fell 3%, its margins compressed, and management is uncertain about the direction. At $50, expected future returns are negative. I'm selling."
A sunk-cost error: "I'm down 50% from the $80 I paid. That's painful. I'll sell if it gets back to $70 to recover some capital."
The distinction is forward-looking fundamentals vs. backward-looking price anchors.
The mental reframe
Instead of thinking "I lost $30 per share," reframe to: "I have $50 cash in a position. Is the best use of $50 to own more of this stock, or to own something else?"
This reframe removes the anchor. You're no longer thinking about what you paid. You're thinking about what you'll earn. If the answer is "something else," sell. The $30 loss is already real. Holding hoping to recover it doesn't undo it; it compounds it.
Common sunk-cost scenarios
Scenario 1: The inherited loser. You inherit 100 shares of a company at $5 per share. It's now at $2. You feel obligated to hold because "you got it for free." But the free cost basis doesn't matter. If $2 per share doesn't promise future returns, sell and redeploy the capital.
Scenario 2: The employee stock that crashed. You received company stock at $50 (during employee stock purchase plan or stock options). It's now $20. You're holding because you "got a good deal" initially. But the initial discount was a gift from the past. The current $20 value is what matters. If the company's outlook is poor, sell.
Scenario 3: The "I'll break even" anchor. A stock falls from $100 to $30. You decide: "If it ever gets back to $80, I'll sell and call it even." But this decision inverts priorities. You're saying: "If the stock rebounds 167%, I'll exit." That's not risk management. That's sunk-cost anchoring.
Sunk costs in other domains
The fallacy isn't unique to investing:
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Sunk college costs: You're halfway through an engineering degree but hate engineering. Sunk-cost thinking says: "I've already paid $60,000; I should finish." Rational thinking says: "I have $60,000 paid (irrelevant) and 4 more years of engineering I'll hate. I should switch majors."
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Sunk relationship costs: You've been in a relationship for 5 years. It's not working. Sunk-cost thinking says: "I've invested 5 years; I should stay." Rational thinking: "I have 50+ years ahead. Do I want to spend them with this person?"
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Sunk time costs: You've watched 8 episodes of a bad show. Sunk-cost thinking says: "I've already invested 8 hours; I should finish the season." Rational thinking: "Do I enjoy this show?" If no, stop.
The role of loss aversion
Sunk-cost fallacy is amplified by loss aversion—the finding that losses feel about twice as bad as equivalent gains feel good. Losing $3,000 feels worse than gaining $3,000 feels good. This asymmetry makes it psychologically painful to "lock in" a loss, even if selling is the right move.
The solution isn't to ignore loss aversion (you can't; it's hardwired). It's to override it with rules. Write in your investment policy: "I sell positions where the thesis breaks, regardless of cost basis or current price." When pain arrives, follow the rule.
Tax-loss harvesting as a reframe
One way to psychologically recover from sunk-cost traps is tax-loss harvesting. You sell the losing position (admitting the loss), but immediately realize a tax loss that saves you money. This reframe—from "loss" to "tax savings"—makes selling feel less punitive.
Example: You sell a position at $50 that cost $80, realizing a $30 loss. At a 20% capital gains rate, this creates $6,000 in tax savings (on 200 shares, $30 × 200 = $6,000 loss × 20%). Suddenly, the sale feels productive, not defeatist.
FAQ
Q: Isn't breaking even a legitimate portfolio goal?
A: No. Breaking even is a reference point, not a financial goal. Your goal is maximizing future wealth. If a position is worth $50 and will likely go to $30, it doesn't matter that you paid $80. Sell.
Q: If I sell and the stock rebounds, won't I regret it?
A: Probably. But regret is not a reason to hold. Regret is the tax you pay for admitting error. Paying the regret cost (selling) is smarter than compounding the error (holding hoping to break even).
Q: How do I know if a loss is temporary (hold) or permanent (sell)?
A: Look at the fundamentals, not the price. Did the business model break? Did competitors overtake? Did management fail? If yes, it's permanent. If no (bear market decline), it may be temporary. Thesis, not price, is the signal.
Q: If I hold a position for 10+ years and it's still down, shouldn't I cut it?
A: Only if the thesis broke. If you bought at $80 and it's at $40 after 10 years, but the business is sound and competitive position intact, there's no sunk cost—only a poor initial valuation or bad luck. Hold or sell based on fundamentals, not emotion.
Q: Is it ever okay to wait for breakeven?
A: Only if the thesis is intact and you believe future returns are positive. "I'll sell at breakeven" is sunk-cost thinking. "I'll hold because the thesis is intact and the business will grow" is forward-looking.
Q: How do I prevent anchoring to cost basis?
A: Don't track cost basis frequently. Review only fundamental metrics: competitive position, margin trends, growth rate, valuation. If these are good, the position is good, regardless of what you paid.
Related concepts
- Anchoring bias: Using a reference point (cost basis) that becomes disproportionately influential in decisions
- Loss aversion: The tendency to feel losses more acutely than equivalent gains
- Disposition effect: Selling winners and holding losers, partially driven by cost-basis anchoring
- Status quo bias: The tendency to hold an investment because you already own it, ignoring new information
- Regret aversion: The desire to avoid admitting a mistake, leading to holding losers
Summary
The price you paid for a stock is irrelevant to whether you should hold or sell it. The only relevant facts are current prospects and future probabilities. Anchoring to cost basis and holding until "breakeven" is a cognitive error that costs investors significant wealth. The solution is simple: sell when the thesis breaks, regardless of price. Accept the loss, harvest it for taxes if possible, and redeploy capital to better opportunities. The money spent is sunk. The decision is forward-looking. Divorcing these two concepts is the essence of clear investing thinking.