Glossary term
Sunk Cost Fallacy
The sunk cost fallacy is the tendency to keep committing to a decision because of money, time, or effort already spent, even when the better choice has changed.
Updated
Read time
What Is the Sunk Cost Fallacy?
The sunk cost fallacy is the tendency to keep committing to a decision because of money, time, or effort already spent, even when the better choice has changed. A sunk cost is something you cannot recover. The fallacy happens when that past cost controls a current decision.
In financial life, sunk costs can show up in investing, business spending, home projects, subscriptions, education choices, and purchases. The hard part is emotional: walking away can feel like wasting what has already been spent, even if staying costs more.
Key Takeaways
- The sunk cost fallacy happens when past unrecoverable costs drive a current decision.
- In investing, it can make someone keep a stock because they already lost money or spent time researching it.
- The right question is what choice makes sense from today forward.
- The bias often works with loss aversion and anchoring bias.
- A fresh-money test can help: would you make the same decision today if you were starting from zero?
How the Sunk Cost Fallacy Shows Up in Investing
An investor may keep holding a stock because they spent months researching it, bought at a higher price, or already waited a long time for the thesis to work. Those facts may explain the emotional attachment, but they do not prove the stock should still be owned.
The current decision should depend on the business, valuation, risk, tax impact, and portfolio role from here. The time and money already spent cannot be recovered by forcing the position to stay in the portfolio.
Why It Can Be Costly
The sunk cost fallacy can keep money, attention, and emotional energy tied to decisions that no longer deserve them. In investing, it can delay selling a broken thesis. In business, it can keep funding a weak project. In household finance, it can make someone keep paying for something because they already paid so much.
Continuing a decision can be rational when the future case is strong. It becomes a problem when the past cost is the main reason for staying.
Example of the Sunk Cost Fallacy
Suppose an investor buys a stock after doing extensive research. The company later reports several quarters of weaker cash flow and repeated dilution. The investor keeps holding because abandoning the position would make all the work feel wasted. The better question is whether the stock deserves to be owned now.
Research is valuable only if it helps update the decision. It should not become a reason to defend the old one.
How to Reduce the Sunk Cost Fallacy
Use a forward-looking question: if you had no money, time, or pride invested in this decision, what would you choose today? Then compare that answer with what you are actually doing.
For stock decisions, pair this with When Should You Sell a Stock?. If the issue is opportunity cost, review Is the Highest-Return Choice Always the Best Financial Move?.
The Bottom Line
The sunk cost fallacy is the tendency to keep committing to a decision because of costs already spent. Better financial decisions focus on what can still be changed: future risk, future return, cash flow, opportunity cost, and fit with the plan.