Sunk Costs Can't Answer the Question You're Asking

A sunk cost is money, time, or effort already spent that cannot be recovered no matter what happens next. That definition sounds harmless — almost too obvious to write down. The fallacy isn't misunderstanding the definition. It's treating something that's mathematically irrelevant to a forward decision as if it were the most important input to it.

The jet that flew for decades because it had already flown

Concorde, the supersonic passenger jet developed jointly by Britain and France, is the textbook case — well-known enough in behavioral economics that "the Concorde Fallacy" is sometimes used as another name for sunk cost fallacy itself. Internal assessments showed years before the program's cancellation that it would never be commercially profitable. It kept flying anyway, for decades, and the billions already invested were explicitly cited as a reason to keep funding it rather than write off the loss. The logic was exactly backwards: the size of the past investment was treated as proof the project was too important to abandon, when the money already spent was, by definition, gone either way.

It feels like loyalty, not like an error

Sunk cost fallacy survives because giving up after a large investment doesn't feel like a rational recalculation — it feels like admitting the investment was wasted, and abandoning something you've defended publicly feels like a personal failure rather than a course correction. Continuing feels responsible, disciplined, even virtuous. Stopping feels like betraying your past self. That's what makes the fallacy so durable: it isn't stupidity. It's a very human confusion between honoring effort already spent and repeating a mistake that's already been made.

A constant can't change which option is better

Here's the part that isn't a psychological suggestion, it's just arithmetic: whichever you choose — continue or quit — the amount already spent is identical on both sides of the comparison. It appears equally in the "continue" scenario and the "quit" scenario, which means it mathematically cancels out of the decision entirely. The only numbers that can actually change which option is better are the cost still ahead and the benefit still ahead — figures about the future, not the past. A constant, by definition, cannot make one option better than another. The past isn't a variable in a forward-looking decision. It's already been paid, in every version of what happens next.

Publicness makes it worse

The more visible a decision was when it was made, the harder sunk cost distorts what happens next — walking away means being seen, by name, as having been wrong. This is why organizations often ride a failing initiative further than any single person would alone: every stakeholder who signed off has their own reason not to be the one who says it should stop, and the group ends up more committed to a bad bet than any individual member would be on their own.

The one-question check

Before continuing to fund, staff, or defend something because of what's already gone into it, ask: if none of that had been spent yet, and I were deciding today with only the costs and benefits still ahead of me, would I choose to start this from scratch? If the honest answer is no, continuing isn't commitment. It's sunk cost, wearing commitment's clothes.