You're forty minutes into a film that is, objectively, terrible. You know it. You could turn it off right now and spend the rest of the evening doing anything else. But you paid £14 for the ticket, or you've already committed forty minutes, and so you stay — grimly, joylessly, determined to get your money's worth. This is the sunk cost fallacy in its most harmless form. It scales up considerably from there.
What is a sunk cost?
In economics, a sunk cost is any cost that has already been incurred and cannot be recovered. The ticket price is gone whether you walk out at the interval or sit through the credits. The years you've put into a career, a relationship, or a failing business venture are spent whether you continue or not. Past investment does not change the future — it only changes how you feel about the future, which is where the trouble starts.
The sunk cost fallacy is the tendency to factor these irrecoverable costs into decisions about what to do next — to keep throwing resources at something not because the future looks promising, but because of what you've already put in. Rational decision-making says: judge every choice purely on its future costs versus future benefits. The past is a sunk cost. It does not get a vote.
Where it shows up
The fallacy is everywhere once you start looking:
- Entertainment: finishing a bad film, book, or game because you paid for it or already started.
- Food: eating past the point of fullness at a restaurant because you paid for the meal.
- Careers: staying in a dead-end job for years because of all the time already invested in that field.
- Relationships: remaining in a relationship that isn't working because of "everything we've been through."
- Gambling: a gambler chasing losses — putting more money in to "win back" what's already gone.
- Business: a company continuing to pour budget into a failing project rather than cutting losses, because the team has already spent two years on it.
The Concorde fallacy: when governments do it
The most cited large-scale example is the Concorde supersonic passenger jet, which gives the phenomenon an alternative name: the Concorde fallacy. Britain and France began developing Concorde jointly in the 1960s. It became clear fairly early that the aircraft would never be commercially profitable: the market was too small, the operating costs too high, and the economics fundamentally difficult. Yet both governments continued funding it for years, in part because they had already committed so much money and national prestige that stopping felt worse than continuing. The plane flew commercially from 1976 until 2003 and never turned a profit for its operators. The prior investment did not make continuing rational — it just made stopping feel unbearable.
Psychologists Hal Arkes and Catherine Blumer demonstrated the sunk cost effect cleanly in a series of experiments published in 1985. In one, participants who had paid more for a ski-resort season ticket were more likely to push through bad weather to use it than those who had paid a discounted price — even though the future experience was identical. The only thing that differed was the past cost. That past cost had no logical bearing on whether the trip was worth taking today. But it changed behaviour anyway.
Why the brain falls for it
The sunk cost fallacy is not stupidity. It is the predictable output of two well-documented cognitive tendencies:
- Loss aversion: Daniel Kahneman and Amos Tversky's prospect theory showed that losses feel roughly twice as painful as equivalent gains feel good. Quitting feels like "confirming" a loss — booking it in the ledger — whereas continuing keeps open the possibility that things will turn around. The mind prefers that ambiguity to the finality of admitting the money or time is gone.
- Consistency and self-image: Most people prefer to see themselves as someone who makes good decisions and follows through on commitments. Quitting can feel like evidence of a mistake, which is uncomfortable. Continuing lets you maintain the story that the original decision was sound.
Both instincts are useful in many contexts — perseverance and commitment are often genuinely valuable. The problem is applying them to situations where the underlying facts have changed and the honest assessment is that the future no longer justifies the cost.
How to actually escape it
Knowing about the sunk cost fallacy does not automatically make you immune to it — but it gives you something to work with. A few practical approaches:
- The fresh-start test: Ask yourself, "If I were making this decision today, from scratch, knowing what I know now, would I choose to begin?" If the answer is no, the prior investment is not a reason to continue. It is simply a fact about the past.
- Judge future costs against future benefits only. Make a short list: what will this actually cost me going forward (time, money, opportunity, wellbeing), and what will I actually get? If the future case doesn't hold up on its own, it doesn't hold up.
- Reframe quitting. Walking away from a bad investment is not wasting what came before — the past is already spent regardless. Quitting is freeing your remaining time and money for something with a better return. The choice is between two futures, not between honouring or wasting the past.
- Pre-commit to exit criteria. Before starting a project, investment, or commitment, decide in advance what conditions would make you stop. Writing this down while you're calm and un-invested makes it much easier to act on later, when the sunk costs are real and the emotional pressure is high.
None of this is a guarantee. The sunk cost pull is strong precisely because it mimics virtues — loyalty, perseverance, not being a quitter. The difference is that genuine perseverance is driven by a clear-eyed assessment of the future. The sunk cost fallacy is driven by the past. The past is a receipt, not a strategy.
Sources & further reading
- Arkes & Blumer (1985) — "The psychology of sunk cost", Organizational Behavior and Human Decision Processes
- Kahneman & Tversky — Loss aversion and prospect theory overview, Behavioral Economics Encyclopedia
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