The sunk cost fallacy: why we keep investing in lost causes

"I've already invested too much to quit now." This sentence is one of the most powerful cognitive traps in existence. It's called the sunk cost fallacy, and it silently governs an enormous number of our decisions: from the relationship we know no longer works, to the work project that keeps burning resources without results.

The sunk cost principle

A sunk cost is any resource — time, money, emotional energy — you've already spent and can no longer recover. Logic would say: what's spent is spent. Decisions should be based only on what will happen from here forward, not on what has already occurred.

But the brain doesn't work that way. Loss aversion — the tendency to perceive losses as more painful than equivalent gains — makes past investment a psychological constraint. Abandoning a project you've invested two years in feels like "throwing away" those two years. Continuing feels like "protecting" them.

The Concorde fallacy

The most famous case is the Concorde, the Anglo-French supersonic aircraft. Halfway through development, it was already clear the project would never be commercially profitable. But the British and French governments continued funding it for years, because the previous investment was too large to be "wasted." The result: billions more burned to avoid admitting that the previous billions were already lost.

This pattern repeats everywhere. The student who continues a degree they hate because "I'm already in my third year." The entrepreneur who pumps money into a startup the market has rejected. The investor who holds free-falling stocks waiting to "at least recover what I put in."

Why it's so hard to escape

The sunk cost fallacy isn't just a logical error — it's a deep emotional mechanism. Exiting a failed investment means three painful things: admitting you were wrong, giving up the possibility of recovery, and facing the judgment (real or imagined) of others.

Moreover, past investment creates identity. "I'm the person who dedicated their life to this project." Abandoning the project feels like abandoning part of yourself.

How DAMM reframes the problem

The DAMM framework offers a structured way out of the sunk cost trap.

Delimitation reframes the central question. Instead of asking "how much have I already invested?", it asks "what can I still lose from here forward?". This temporal shift — from past to future — neutralizes the sunk cost mechanism. The only relevant question is: given where I stand today, what do I risk by staying?

Asymmetry makes the real comparison visible. If you continue, what are the realistic gains? If you exit, what are the actual losses? We often discover that continuing has a high future cost and uncertain gain, while exiting has a manageable immediate cost and frees resources for better opportunities.

Minimum Move reduces the fear of exit. You don't have to abandon everything at once. You can reduce your commitment by 50% for a month and see what happens. You can pause the project for three months. You can stop actively investing without yet liquidating. Gradual exit is almost always possible, and almost always less traumatic than we imagine.

Practical examples

The struggling startup. You founded a company two years ago, invested 100,000 euros and all your time. Customers aren't coming. The market isn't responding. Continuing means investing another 50,000 and another year. The question isn't "how do I recover the 100,000?" (that's a sunk cost). The question is: "Will the next 50,000 euros and the next year of my life produce a better return here or elsewhere?"

The losing investment. You bought stocks at 100 euros, now they're worth 60. Holding them "until they bounce back" is logical only if you believe that stock will rise more than any alternative you could invest those 60 euros in. If you don't believe that, you're paying the sunk cost fallacy.

The relationship that isn't working. "After eight years I can't throw it all away." You're not throwing away eight years — those are already lived. You're deciding how to live the next eight. This reframing changes everything.

The golden rule

Every time you find yourself thinking "I've already invested too much to stop," pause. You're using the past to justify the future. Start from zero: if today you hadn't already invested anything, would you choose to begin? If the answer is no, the sunk cost is deciding for you.