Sunk Cost Fallacy: Meaning, Examples and the Relationship Question

What is the sunk cost fallacy?

A sunk cost is a cost that has already been paid and cannot be recovered: the nonrefundable concert ticket, the hours spent on a plan, the money already put into an old car. The sunk cost fallacy is letting that past cost drive a decision about the future. Economists put it simply: a rational choice depends on what each option will cost and deliver from now on, because the past cost stays the same no matter which option you pick.

Psychologists Hal Arkes and Catherine Blumer described the pattern in a 1985 paper called "The psychology of sunk cost": people show a stronger tendency to continue an endeavor once they have invested money, effort or time in it. It is sometimes called the Concorde fallacy, after the supersonic jet that kept receiving funding long after its commercial prospects looked poor.

Everyday examples of the sunk cost fallacy

Sunk cost reasoning is everywhere once you start looking for it. A few familiar versions:

• Going to a concert you no longer want to attend, in the rain, while sick, because the tickets were expensive.
• Finishing a terrible movie because you already watched an hour of it.
• Pouring repair money into a car that keeps breaking because you just paid for a new transmission.
• Sticking with a vacation plan that nobody is enjoying because the deposit is already paid.
• Refusing to change a project that clearly is not working because the team spent three months on it.

Sunk Cost Fallacy examples

How sunk costs show up inside arguments

In every one of those cases, the question that matters looks forward: from here, which option gives the better result? Arguments have sunk costs too. After forty minutes of defending a position, backing down feels like wasting the forty minutes. So people dig in, not because the evidence got stronger but because they have invested in being right. You hear it in lines like "we've been arguing about this all night, I'm not giving up now" or "I already told everyone we're going, so we're going."

It also appears as a pressure tactic: "I spent all afternoon planning this, so you have to come." The effort was real and deserves appreciation. But effort spent is not a reason the plan is right for tonight. Saying both of those things at once, "thank you for planning, and I still can't come," is often the fairest answer. If the whole argument is starting to feel like a battle you cannot leave, our guide on how to stop arguing may help.

The sunk cost fallacy in relationships

"We've been together five years" is one of the most common sunk cost sentences, and it deserves care rather than a slogan. Researchers have asked whether the sunk cost effect appears in committed relationships too; a paper by Rêgo, Arantes and Magalhães in Current Psychology studied exactly that question. The general point is easy to see: years together can feel like an investment you would lose by leaving.

But the past in a relationship is not only a sunk cost. Shared history is also information and, often, ongoing value: you know each other, you have built routines, friendships, finances and sometimes a family. Those things can make the future together better, and weighing them is not a fallacy. The fallacy is narrower. It is staying, or refusing to change anything, purely because walking away would "waste" the years already spent, without asking what the years ahead are likely to look like.

This page will not tell anyone to stay or to leave; that decision depends on far more than one reasoning error. A more useful question than "how much have we put in?" is "what do we each want the next year to look like, and what would need to change for that?" A couples therapist can help partners have that conversation honestly. If a relationship involves fear, threats or control, the past investment is not a reason to stay unsafe, and talking to a support service or trusted person comes first.

When past investment does matter

Not every appeal to past effort is a fallacy. Past effort can change what the future costs: if a project is 95 percent finished, the remaining 5 percent is cheap, and finishing may be the right call. Past commitments can also create real obligations, like a promise to a friend or a contract. And some philosophers argue that caring about past investment can be reasonable in certain cases, for instance when it reflects your values or the meaning you have built into something.

The question to ask is whether the past is being used as information about the future, or as a weight you are afraid to put down. The first is good reasoning. The second is the sunk cost fallacy.

How to respond to sunk cost reasoning

Separate gratitude from decision. Acknowledge what the other person invested, sincerely, and then bring the conversation to the future: "Given where we are now, what's the best option?" If you are the one stuck, try imagining you are starting fresh today with the same options: which would you pick? That thought experiment strips away the sunk cost without dismissing what it meant. Watch for the opposite trap too: "we already lost so much, we can't stop now" often travels with a false dilemma that hides other choices.

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