Sunk Cost Fallacy

Why we throw good money after bad and can't walk away from failing investments.

Plausibility Index: 4.8/10 — Rock Solid

Extensively documented across psychology and economics with robust experimental evidence and clear real-world manifestations.

The quick version

You've probably fallen for this one: staying in a bad movie because you paid for the ticket, or continuing a doomed project because you've already spent months on it. The sunk cost fallacy tricks us into thinking past investments justify future ones, when really, only future costs and benefits should matter for good decisions.

Origin story

The sunk cost fallacy didn't get its name from economists sitting in ivory towers—it emerged from watching real people make consistently irrational decisions. In the 1960s, researchers noticed something puzzling: people would often continue losing strategies simply because they'd already invested time, money, or effort.

The breakthrough came when psychologists Hal Arkes and Catherine Blumer ran a series of experiments in the 1980s. In one famous study, they gave people season tickets to a theater series. Some participants paid full price, others got discounts, and some received free tickets. The twist? The researchers made the first few performances deliberately boring. Who do you think kept showing up despite the terrible shows? The people who paid full price, of course.

This wasn't just about money—it was about psychology. The researchers realized we have a deep, almost primitive aversion to 'wasting' what we've already spent. We treat sunk costs as if they're still recoverable, even though they're gone forever. The name 'sunk cost fallacy' stuck because it perfectly captured the irony: the very costs that should be irrelevant to our decisions (because they're already 'sunk' like a ship) become the driving force behind our choices.

What made this discovery so important wasn't just that it explained individual bad decisions—it explained massive institutional failures too. The Concorde supersonic jet program continued for years after it became clear it would never be profitable, largely because Britain and France had already invested so much. Vietnam War escalation followed similar logic. The sunk cost fallacy, it turned out, wasn't just a quirky bias—it was a fundamental flaw in how humans think about investment and commitment.

How it works

The sunk cost fallacy works by hijacking our natural loss aversion and turning it against us. Think of it like this: your brain treats every dollar you've spent, every hour you've worked, every ounce of effort you've invested as still somehow 'yours'—even though it's gone forever. When you consider abandoning a project, your brain screams 'But what about all that work we already did?'

Here's the cruel irony: the more you've already invested, the stronger the trap becomes. It's like quicksand for decision-making. A rational person should only care about future costs and benefits when deciding whether to continue something. If a project will cost another $100,000 and only generate $50,000 in value, you should quit—regardless of whether you've already spent $10,000 or $10 million. But our brains don't work that way.

The fallacy gets amplified by what psychologists call 'commitment escalation.' Once we've publicly committed to something—told our boss about the project, announced our business idea to friends, bought that expensive gym membership—walking away feels like admitting failure. We'd rather double down than face the psychological pain of acknowledging a mistake.

The trap is particularly vicious because it often involves legitimate emotions. That time you spent learning to play guitar wasn't actually wasted if you enjoyed it or learned something. But when you continue taking lessons you hate just because you've 'already invested so much,' you've fallen into the fallacy. The key insight is learning to distinguish between honoring past investments and being enslaved by them.

Real-world examples

The Concorde's $15 Billion Mistake

The Concorde supersonic passenger jet is perhaps history's most expensive example of the sunk cost fallacy. By the early 1970s, it was clear the project would never be commercially viable—fuel costs were too high, noise restrictions limited routes, and demand was minimal. But Britain and France had already invested billions and couldn't bear the thought of 'wasting' it all. They kept pouring money in for another decade, ultimately spending over $15 billion (in today's money) on a program that operated at a loss for most of its life. The planes finally retired in 2003, having carried more prestige than passengers.

Netflix's $200 Million 'Bright' Sequel

When Netflix spent $90 million on the Will Smith fantasy film 'Bright' in 2017, critics savaged it as one of the worst movies ever made. Audiences weren't much kinder. The rational response? Cut losses and move on. Instead, Netflix immediately announced they were spending another $90+ million on a sequel, largely because they'd already committed so much to the franchise. The sequel was quietly canceled years later after the sunk cost reality finally set in, but not before millions more were spent on development.

Your Last Relationship

You probably stayed in a relationship longer than you should have because you'd already invested so much time and emotion. Maybe it was the college relationship that lasted through senior year despite obvious incompatibility, or the friendship you maintained for years after it stopped being fulfilling. We tell ourselves 'But we've been together for three years!' as if time invested guarantees future happiness. The sunk cost fallacy in relationships is particularly painful because the 'investment' feels so personal—but those shared memories don't justify staying in something that no longer serves you.

Criticisms and limitations

The biggest criticism of sunk cost fallacy research is that it sometimes oversimplifies complex decisions. Critics argue that what looks like irrational 'sunk cost thinking' might actually be rational when you consider factors like reputation, learning, or signaling commitment to others. If you quit every project the moment it gets difficult, people might stop trusting you with important responsibilities.

There's also the 'completion value' argument. Sometimes finishing something has intrinsic worth beyond pure cost-benefit analysis. The sense of accomplishment from completing a difficult degree or finishing a challenging book might justify the 'irrational' decision to continue even when the pure economics don't add up.

Another limitation is cultural context. Research shows the sunk cost fallacy is stronger in some cultures than others, particularly those that highly value persistence and commitment. What Western economists label as 'irrational' might reflect different cultural values about honor, consistency, and long-term thinking.

Perhaps most importantly, the research sometimes ignores that quitting has real costs too—not just financial, but psychological and social. The shame of admitting failure, the loss of credibility, the impact on team morale—these aren't always irrational considerations, even if they're hard to quantify.

Related theories

Loss Aversion

The psychological foundation underlying sunk cost fallacy—we feel losses more intensely than equivalent gains.

Commitment and Consistency Bias

Explains why we continue failing courses of action to appear consistent with past decisions.

Escalation of Commitment

The organizational version of sunk cost fallacy, where groups double down on failing strategies.

Go deeper

Thinking, Fast and Slow by Daniel Kahneman (2011) — The Nobel laureate's accessible exploration of cognitive biases including sunk costs.

Predictably Irrational by Dan Ariely (2008) — Engaging experiments showing how sunk costs and other biases shape our decisions.

The Sunk-Cost Fallacy in Penny Auctions by Arkes & Blumer (1985) — The foundational research that named and defined the sunk cost fallacy.

Footnotes

1. The term 'sunk cost' comes from accounting, where it refers to costs that have already been incurred and cannot be recovered.
2. Studies show the sunk cost fallacy is stronger when the initial investment was larger and when the person made the investment decision themselves.
3. Interestingly, we're more susceptible to sunk cost fallacy with time investments than money investments, possibly because time feels more personal and irreplaceable.