The sunk cost fallacy is the tendency to keep investing time, money, or effort into a decision because of what's already been spent on it, rather than because of what the choice will actually deliver going forward. Economists call spending that can't be recovered a 'sunk cost' for exactly that reason — it's gone regardless of what happens next — yet people routinely let it steer the decision anyway.
Economists Richard Thaler and Hal Arkes helped popularize the term in the 1980s, building on research showing that people feel losses more sharply than equivalent gains, which is part of why walking away from a bad investment can feel like admitting defeat.
Why Past Investment Feels Like It Should Count
Where It Shows Up and How to Catch It
Rationally, only future costs and benefits should guide a decision — money already spent on a doomed project, a strained relationship, or an unused gym membership can never be recovered by continuing. But abandoning something makes the original investment feel wasted, and that emotional sting often outweighs the logic of simply cutting losses.
Companies fall into it when they keep funding a failing product line because of years of prior investment, governments fall into it with stalled infrastructure projects, and individuals fall into it by sitting through a bad film or finishing a meal just because they already paid for it. One practical fix behavioral economists suggest: treat any 'should I continue' question as if you were deciding fresh today, with no memory of what you already spent.
Sources
- Wikipedia — overview of sunk cost reasoning in economics and psychology
- Investopedia — explanation of sunk costs and the fallacy in financial decisions
- Psychology Today — psychological explanation of why sunk costs influence decisions
FAQ
Is the sunk cost fallacy the same as being persistent?
No — persistence continues because the future payoff still looks worthwhile, while the sunk cost fallacy continues mainly because of what has already been spent, regardless of the outlook ahead.
Do animals show sunk-cost-like behavior too?
Some studies on mice and rats suggest similar patterns in foraging decisions, though researchers still debate whether that reflects the same reasoning error humans make.
How can I avoid falling for it?
Ask only whether you would choose to start this again today, knowing what you know now — if the answer is no, the money or time already spent should not change it.
About the Author
We reference Wikipedia, Investopedia, and Psychology Today to explain the background and current understanding of this topic.
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