Sunk Cost Fallacy

Every resource you have already spent — every dollar, every hour, every ounce of emotional energy — is gone. It cannot be recovered regardless of what you decide next. The sunk cost fallacy is the systematic error of letting those irrecoverable expenditures influence future decisions, as though continuing to invest can somehow redeem what has already been lost.

The rational principle is stark: only future costs and future benefits should inform current choices. Past expenditures are economically irrelevant. A dollar spent yesterday has exactly zero bearing on whether spending another dollar today is wise. The decision framework should be identical whether you have invested $10 million or $10 in a failing venture — what matters is the expected return on the next dollar, not the accumulated weight of previous ones.

Economists have understood this since at least Alfred Marshall's Principles of Economics in 1890. The insight is trivial to grasp intellectually and nearly impossible to execute emotionally. Ask a room of MBA students whether sunk costs should influence decisions and every hand goes up to say no. Put those same students in a simulation where they've already "invested" significant resources in a failing project, and a majority will escalate their commitment. The gap between knowing the principle and living it is the entire story of the sunk cost fallacy.

The most famous case study in sunk cost reasoning carries the bias's alternate name. The Concorde supersonic jet — a joint venture between the British and French governments — consumed approximately $2.8 billion in development costs (over $13 billion in 2024 dollars) across two decades of engineering. By the early 1970s, internal analyses at both governments had concluded the aircraft would never achieve commercial viability. Sonic boom regulations, fuel consumption rates, and narrow passenger capacity guaranteed that airlines would not order enough planes to recoup the investment. Both governments knew this. Both continued funding.

The reasoning was transparent and irrational: they had already spent too much to stop. Cancellation meant accepting the loss publicly — admitting that billions had been wasted. Continuation preserved the fiction that the investment might eventually pay off. Only 14 Concordes entered commercial service. The last flight landed at Heathrow on October 24, 2003. Economists coined the term "Concorde fallacy" to describe the pattern, and it remains the purest example of the phenomenon at sovereign scale.

The same logic drove the escalation of the Vietnam War. Robert McNamara, U.S. Secretary of Defense from 1961 to 1968, later acknowledged in his 1995 memoir In Retrospect that by 1965, senior officials had serious doubts about the war's winnability. The United States had already deployed 184,000 troops and spent billions. The sunk cost argument — "we cannot let these sacrifices be in vain" — became the political and psychological justification for escalation. Troop levels peaked at 549,500 in 1969. Total U.S. expenditure exceeded $140 billion (roughly $1 trillion in 2024 dollars). The cost of the war wasn't incurred because the strategy was working. It was incurred because the prior costs made withdrawal feel like betrayal.

Hal Arkes and Catherine Blumer formalised the phenomenon in their 1985 paper "The Psychology of Sunk Cost," published in Organizational Behavior and Human Decision Processes. Through a series of ten experiments, they demonstrated that people who had invested more in an activity were more likely to continue it — regardless of whether the activity was producing returns. In one landmark experiment, they sold Ohio University theatre season tickets at three randomly assigned prices — full price ($15), a small discount, and a large discount. Over the following months, full-price buyers attended significantly more performances than discounted buyers. The shows were identical. The enjoyment was identical. The only difference was how much each person had paid — and that payment, already made, should have been irrelevant to the decision of whether to attend on any given evening. A $15 ticket to a bad play keeps more people in their seats than a free ticket to the same bad play. The investment creates a psychological debt that only continued participation can discharge.

The corporate version is more expensive. Kodak invested over $5 billion in digital photography research and development between 1975 and 2003 — more than any competitor. Steve Sasson, a Kodak engineer, built the first digital camera prototype in 1975. The company held thousands of digital imaging patents. Kodak had every technical advantage needed to lead the digital transition. The accumulated investment in film infrastructure — factories, supply chains, distribution partnerships, brand positioning — became an anchor. Each dollar sunk into the film ecosystem reframed digital as a threat rather than an opportunity. Kodak filed for bankruptcy in January 2012, killed not by a lack of technology but by an inability to abandon the past.

The fallacy operates at every level of human decision-making. A PhD student who has spent five years on a dissertation topic continues despite losing interest because abandoning it means "wasting" those years. A CEO who championed an acquisition continues defending it after integration fails because reversing course means admitting the original decision was wrong. A government that has spent $400 billion on a fighter jet programme refuses to cancel it despite decade-long delays and ballooning costs because the prior spending creates political pressure to see it through. In each case, the past consumes the future. The sunk cost doesn't change what the right decision is. It changes how painful the right decision feels.

The asymmetry between knowing and doing is the entire subject of the sunk cost literature. Every CEO can articulate the principle in a board meeting. Almost none can execute it when the $200 million project they championed is failing and the board is watching. The fallacy is not an information problem. It's an execution problem — and the execution gap widens in direct proportion to the size of the prior investment, the public visibility of the commitment, and the personal identification of the decision-maker with the original choice.