# Sunk Cost Fallacy

> The sunk cost fallacy keeps traders in bad positions because of money already lost. Learn how it works, how it differs from loss aversion and how to break it.

Source: https://learn.tradelabsai.com/psychology/sunk-cost-fallacy/  
Track: Trading Psychology · Level: Intermediate · Updated: 2026-10-03  
Publisher: TradeLabs AI (https://tradelabsai.com). Education, not financial advice.  
Cite as: TradeLabs Learn, "Sunk Cost Fallacy", https://learn.tradelabsai.com/psychology/sunk-cost-fallacy/

The sunk cost fallacy is the tendency to keep investing time, money or effort into something because of what has already been spent, rather than because of what is likely to happen next. A sunk cost is money that is gone and cannot be recovered whatever you decide. Rationally, it should play no part in the decision. In practice, it plays a huge part, and trading is full of examples.

## The idea in one sentence

The only question that matters for an open trade is: "Given everything I know now, is this the best use of this capital from here?" The price you paid, the hours you spent researching and the loss you are currently sitting on do not change the answer.

## How it shows up in trading

| Thought | Why it is the sunk cost fallacy |
|---|---|
| "I've lost $2,000 on this, I can't sell now" | The $2,000 is gone whether you sell or hold |
| "I'll hold until I get back to break even" | The market does not know or care about your entry price |
| "I spent weeks researching this stock, it has to work" | Research time is spent; it does not change the outlook |
| "I've paid for this course or tool, so I must use this strategy" | The cost is gone; only future results matter |
| "I've already averaged down twice, one more time" | Each add is a new decision and should be judged on its own |

**Example: Two traders, one stock**
Trader A bought a stock at $50; it is now $35. Trader B has no position and the stock is $35. Both have the same information about the company's future. If Trader B would not buy the stock at $35, then Trader A should ask why they are effectively choosing to own it every day by continuing to hold. The only difference between them is a sunk cost, which should not affect the decision.

## Sunk cost vs related biases

These biases often travel together, but each describes a different piece of the problem:

- **[Loss Aversion](https://learn.tradelabsai.com/psychology/loss-aversion/)** explains why losses hurt so much that we avoid realising them.
- **[Disposition Effect](https://learn.tradelabsai.com/psychology/disposition-effect/)** is the visible result: selling winners too early and holding losers too long.
- **[Anchoring](https://learn.tradelabsai.com/psychology/anchoring/)** makes the entry price feel like a meaningful level.
- **Sunk cost fallacy** is the reasoning that ties them together: "I've already put so much in."

## Averaging down

Adding to a losing position is not always a mistake. Some planned strategies scale in at predefined levels with total risk set in advance. The sunk cost version is unplanned: adding to a loser to lower the average price so that break even feels closer, without a fresh reason to buy. This can turn a small mistake into a large one, because each add increases exposure to an idea the market is already disagreeing with. See [Scaling In and Pyramiding](https://learn.tradelabsai.com/position-management/scaling-in-and-pyramiding/).

## Beyond individual trades

The sunk cost fallacy also affects bigger decisions:

- Sticking with a strategy that has clearly stopped working because of the time spent building it. See [Why Strategies Fail](https://learn.tradelabsai.com/research/why-strategies-fail/).
- Keeping a broker, platform or subscription because of past payments.
- Continuing to trade a market you have studied extensively even after evidence shows you do not have an edge there.
- Refusing to close a trading account in drawdown because closing it would make the loss feel final.

In each case, the honest question is the same: what is the best choice from here, with what you now know?

## How to break the sunk cost fallacy

1. **Use the fresh eyes test:** "If I had cash instead of this position, would I buy it now?"
2. **Set exits before entry** so the decision is made before any loss exists. See [Stop Loss Strategies](https://learn.tradelabsai.com/risk/stop-loss-strategies/).
3. **Plan any scaling in advance** with a total risk limit. See [Position Sizing](https://learn.tradelabsai.com/risk/position-sizing/).
4. **Separate effort from outcome:** research time is a learning cost, not a reason to hold.
5. **Review closed trades** to see how often holding losers made them worse. See [Post-Trade Analysis](https://learn.tradelabsai.com/start-here/post-trade-analysis/).
6. **Hide the entry price** in your platform's position display if it helps you focus on current value.

## Common mistakes

- **Holding to break even** rather than to a planned exit.
- **Unplanned averaging down** on losing trades.
- **Keeping a failed strategy** because of the work already put into it.
- **Trying to win back losses quickly,** which slides into [Revenge Trading](https://learn.tradelabsai.com/psychology/revenge-trading/).

## Frequently asked questions

### What is the sunk cost fallacy in trading?

Making decisions based on money or effort already spent and unrecoverable, such as holding a losing trade because of the loss already taken.

### Is averaging down a sunk cost fallacy?

It can be. Planned scaling with fixed total risk is a strategy; unplanned adding to a loser to feel closer to break even is the fallacy.

### How do I stop the sunk cost fallacy?

Ask whether you would enter the position today with fresh cash, set exits before entering and judge each decision on future prospects only.

Next, learn how one number can take over your judgement: [Anchoring](https://learn.tradelabsai.com/psychology/anchoring/).

## Sources

- Wikipedia, [Sunk cost](https://en.wikipedia.org/wiki/Sunk_cost)

## Continue learning

- Next lesson: [Anchoring](https://learn.tradelabsai.com/psychology/anchoring/)
- Previous lesson: [Gambler's Fallacy](https://learn.tradelabsai.com/psychology/gamblers-fallacy/)
- Related: [Gambler's Fallacy](https://learn.tradelabsai.com/psychology/gamblers-fallacy/): The gambler's fallacy is believing past random outcomes change future odds. Learn how it shows up after streaks and in prediction markets, and how to avoid it.
- Related: [Loss Aversion](https://learn.tradelabsai.com/psychology/loss-aversion/): Loss aversion means losses feel about twice as painful as equal gains feel good. Learn the research, how it damages trading and practical ways to counter it.
- Related: [Disposition Effect](https://learn.tradelabsai.com/psychology/disposition-effect/): The disposition effect is the habit of selling winning trades too early and holding losers too long. Learn the research, what it costs and how to reverse it.
- Related: [Anchoring](https://learn.tradelabsai.com/psychology/anchoring/): Anchoring makes traders rely too heavily on one reference number, like an entry price or an old high. Learn how it distorts decisions and how to adjust properly.
- Related: [Scaling In and Pyramiding](https://learn.tradelabsai.com/position-management/scaling-in-and-pyramiding/): Scaling in builds a position in parts; pyramiding adds to winners as they move your way. Learn safe pyramiding rules, examples and why averaging down differs.
- Related: [Revenge Trading](https://learn.tradelabsai.com/psychology/revenge-trading/): Revenge trading is trying to win back losses fast with bigger or unplanned trades. Learn the warning signs, why the brain does it and rules that stop the spiral.