Topics Mind and behavior

What is the sunk cost fallacy?

The sunk cost fallacy is the habit of continuing with something because of what you have already put into it, such as money, time, or effort, even when the future looks worse than the alternatives. A sunk cost is one that is spent and cannot be recovered. Classic economics says only future costs and benefits should drive a decision, because the past is the same whichever way you choose.

What makes it interesting is that it feels like a virtue. Finishing the meal, sitting through the bad movie, staying with the failing project: these look like persistence and loyalty. Researchers have proposed several explanations, including a dislike of wasting things and a wish to avoid admitting a mistake, but how much each one contributes is still debated. It also does not mean all persistence is irrational. Past investment can sometimes be a useful clue about what is ahead.

An episode would walk through everyday examples, the logic of why sunk costs should not matter, and the cases where the line gets blurry. bre is an app whose hosts are AI, so they can be wrong, and you can press Talk to ask a question about your own situation as it goes.

What a bre episode would cover

An outline of the episode bre would make for this question. Every episode is written fresh when you ask, so yours will differ.

  1. What counts as a sunk costA plain definition, with ordinary examples like a nonrefundable ticket or a half-read book. The key test: would you choose this again, starting from today?
  2. Why the past should not voteThe economic argument for ignoring spent costs, and why only what happens next can change with your choice.
  3. Why it feels so naturalLoss aversion, a dislike of waste, and the wish to stay consistent. Which of these matters most is still argued over.
  4. Where it shows up in real lifeRelationships, careers, projects, investments, and big public programs. Also the idea of escalating commitment, where people double down.
  5. When past effort is a real clueNot every case is a fallacy. Sometimes earlier investment signals progress, reputation, or real switching costs.
  6. Ways people try to step backQuestions like what you would advise a friend, or whether you would start this today. Described as ideas, not advice.

How the episode might open

A sample exchange between two of bre’s AI hosts, bre and Cal. Both are AI; this is written by AI, as every bre episode is.

  1. breAI host

    Say you buy a concert ticket, and the night comes, and there's a storm, and you feel awful. Do you go?

  2. CalAI host

    Honestly? I go. I paid for it. I'd be sitting there soaked and miserable, but I'd have gotten my money's worth, right?

  3. breAI host

    Okay, here's the part nobody tells you. You've paid either way. The money is gone whether you go or stay home.

  4. CalAI host

    Huh. So the ticket is just a fact about the past. The only real question is whether tonight is better with the storm or without it.

  5. breAI host

    Exactly. That's the sunk cost fallacy in one picture: letting a spent cost steer a choice it can't change.

  6. CalAI host

    But hold on, how does that actually work? Because it doesn't feel like a mistake. It feels like being responsible, like not wasting something.

  7. breAI host

    That's the trap. It's dressed up as a virtue. And I don't know if one single reason explains it. Researchers have a few candidates.

  8. CalAI host

    Then let's go through them, and figure out when sticking with something is smart and when it's just a very expensive habit.

Questions people also ask

What is an example of the sunk cost fallacy?
Finishing a bad meal because you paid for it is a common one. The money is spent whether you eat or not, so the real question is whether eating more is worth it. The same pattern appears with long projects, subscriptions, and relationships.
Why do people fall for the sunk cost fallacy?
Several explanations are proposed: dislike of waste, loss aversion, wanting to seem consistent, and reluctance to admit a mistake. Researchers still debate how much each one matters, and it likely varies from person to person and situation to situation.
Is the sunk cost fallacy always irrational?
Not always. Past investment can carry information, such as how far along something is, or it can bring real costs of quitting like reputation or contracts. The fallacy is specifically letting the unrecoverable past outweigh what the future offers.
How is it different from cognitive dissonance?
The sunk cost fallacy is a pattern in decisions: continuing because of past investment. Cognitive dissonance is the discomfort of holding conflicting beliefs or actions, which can help explain why people avoid admitting a past choice was a mistake.

Related topics

More: all 300 topics, mind and behavior, or the longer reads on /learn.

bre’s hosts are AI, and every episode is generated, so they can be wrong: check anything that matters. This page outlines what an episode would cover. It is for interest and learning, not medical, financial or legal advice.