The sunk cost fallacy is the mistake of letting money, time, or effort you cannot recover determine whether you continue with something. The better question is what each option will cost and deliver from this point forward. That usually means comparing the likely future benefits, costs, risks, and best alternative—not trying to justify what you have already spent.
What is the sunk cost fallacy?
A sunk cost is a cost already incurred that cannot be recovered. The sunk cost fallacy occurs when someone continues a behavior or project because of resources already invested, rather than because continuing is the best choice now. BehavioralEconomics.com traces a widely used definition to Arkes and Blumer (1985); the University of Chicago describes the related pattern as continuing to invest in a losing project because so much has already been invested (BehavioralEconomics.com; University of Chicago News).
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In the basic decision model, the irrecoverable past cost is the same whether you continue or stop, so it is not a future benefit of continuing. The choice should ordinarily turn on expected consequences from now on. This is not a rule to abandon anything that has become expensive: future value, new information, and real constraints can all matter.
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What are examples of the sunk cost fallacy?
Eating past the point of enjoyment
You have eaten enough but keep going because the meal was expensive and you want to “get your money’s worth.” The purchase price is already paid. The decision now is whether the remaining food is worth the likely enjoyment and discomfort of eating it.
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Driving to an event in dangerous weather
You drive through hazardous conditions because you have already bought a ticket. The ticket price cannot be recovered, but the risks of the trip and the value of attending are still ahead. Those are the relevant considerations—not a hope that the journey will somehow make the ticket cost disappear.
Choosing how to use a prepaid ticket or service
A theatergoer may choose a play over a more appealing dinner because the ticket is already paid for. This is a utilization decision: choosing between current alternatives when one option has already been purchased. The prepaid item can feel like it deserves extra weight even though the choice is about how to spend the evening now.
Putting more resources into a troubled project
An organization may keep funding a project because it has already spent heavily on it. A scholarly review uses Concorde development as an example of additional funds being justified by a large prior investment despite uncertain financial success; that brief example is not a complete historical account. This is a progress decision: whether to allocate further resources to an existing project (Business Research review).
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Staying on a career path because of years already invested
Someone may remain in a career chiefly because of years spent training or working in it, even as new evidence suggests it is no longer a good fit. The NIH Office of Intramural Training & Education discusses career choices as a setting where commitment to past decisions can overshadow new information. The page notes that its views do not necessarily represent NIH or the federal government (NIH OITE).
How to decide whether to continue, stop, or switch
Use the same forward-looking questions for each option. First identify what kind of decision you are making: using something already paid for, or investing additional resources in a project. Research reviews treat these as different decision types, and the distinction helps keep the comparison clear.
| Question | Continue | Stop or switch |
|---|---|---|
| Expected future benefits | What value is still likely if I continue? | What value might I gain from stopping or choosing the alternative? |
| Future costs and risks | What further money, time, effort, or risk is required? | What costs, risks, or losses follow from stopping or switching? |
| Opportunity cost | What is the best alternative I give up by continuing? | What is the best use of those resources if I stop? |
| New evidence | What evidence now supports continuing? | What evidence now supports changing course? |
| Real constraints | What limits on time, money, or obligations shape this option? | What limits or consequences make stopping difficult or impractical? |
Do not count an irrecoverable payment as a future benefit. But include genuine future consequences: a cancellation fee, a contractual obligation, the value of work already completed, or a realistic limit on available time or money. The point is to separate what is gone from what still changes depending on your choice.
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How to avoid the sunk cost fallacy
- Name the past cost. Identify the money, time, or effort already invested. Ask whether any of it can actually be recovered. If not, do not treat it as a benefit you will receive by continuing.
- Reset the decision. Ask, “If I were making this decision today, knowing what I know now, which option would I choose?” This helps separate the current choice from the desire to defend an earlier one.
- Compare the futures. Consider expected benefits, costs, risks, and the opportunity cost of the best alternative. Include real constraints such as available time or money, rather than pretending they do not exist.
- Set a review point. Decide what new evidence would change your mind and when you will revisit the choice. This makes it easier to tell a reasoned update from continuing only because you have already committed.
- Notice the emotion. Stopping can feel like accepting a loss, and commitment can make a past choice feel harder to question. Those feelings are worth acknowledging, but they do not establish that continuing is best.
These steps are a reflection tool, not a guaranteed cure. NIH OITE says the fallacy cannot be completely avoided, while recognizing its influence and making a new decision based on new data can help.
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The simple rule that sunk costs are irrelevant has important limits. A past investment may provide information about a project, or the broader choice may involve reputational concerns, financial constraints, or limited time. Economists Sue H. Mialon and R. Preston McAfee argue that reacting to past costs can be rational in a range of such situations; a model by Sandeep Baliga and Jeffrey C. Ely treats sunk costs as potentially informative when decision-makers have limited memory about why a project began (Mialon and McAfee; Baliga and Ely).
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The practical distinction is whether history changes the outlook or constraints now. For example, earlier work may reveal useful information about a project’s prospects, or abandoning it may create a real future cost. Consider those consequences directly. Do not continue merely to “make back” an irrecoverable cost.
What research says—and what it does not
A 2015 meta-analytic review in Business Research examined literature from 1976 to 2013. It found evidence of a sunk-cost effect in both utilization decisions and progress decisions, while also warning that studies have not always used consistent definitions or kept these questions separate. That limits how confidently results can be compared or generalized. In the studies analyzed, time attenuated the effect in utilization decisions, and the observed effect was stronger among younger people or students. The review did not support the claim that greater familiarity with economic decision-making, such as economic education, effectively reduces the effect. These are findings about the reviewed studies, not universal predictions about every person or choice.
There is no single prevalence figure established here for how often people fall for the bias. Stanford Report’s January 28, 2026 coverage of neuroscience research involving mice reports that dopamine release in the striatum was influenced by reward size and also increased with the effort cost of acquiring the reward. That is background on how effort and reward may be valued, not a way to diagnose your own decision-making or a proven method for avoiding the fallacy (Stanford Report).
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