Governments kept funding a supersonic passenger jet that everyone involved knew would never turn a profit, for one reason alone: they had already spent too much to stop.

The Concorde programme, a joint effort between Britain and France to build an aircraft that could cross the Atlantic faster than sound, ran for years even as the evidence grew clear that the economics didn't work. The cost of building and flying it far exceeded what airlines could ever charge passengers. Officials knew this, some of them fairly early. The programme continued anyway.

The reasoning offered, again and again, was some version of the same sentence: too much has already been invested to stop now. This is almost word for word the origin of a term economists still use today: the sunk cost fallacy, named directly after Concorde's own history.

The idea is simple to state and hard to resist. Money already spent is gone either way. It can't be recovered by continuing, and it isn't protected by continuing either. The only question that should matter is whether continuing makes sense from this exact moment forward — with the past spending treated as irrelevant.

And yet the past spending never feels irrelevant. It feels like a debt owed, a reason continuing is somehow deserved, as though stopping now would make the earlier cost a waste in a way that continuing wouldn't.

A trader holding a losing position lives a small version of Concorde almost every week. The original reason for the trade may have stopped applying entirely. But the money already committed pulls at the decision anyway, whispering that selling now would make the loss final — as if holding on somehow keeps it merely theoretical.

Underneath this sits a quieter fear too: the fear of regret. Sometimes it's not the loss itself people are avoiding, but the feeling of having to admit the call was wrong — a feeling many people will pay a real cost to postpone.

The fix is the one Concorde's own accountants eventually made, decades too late: ask only what the position is worth from here, as if you were being offered it fresh today, with no memory of what it once cost to get in. Everything already spent has no vote in what happens next.