Notice how rarely anyone is argued out of the sunk cost, and how often they are simply moved past it by a change in circumstance. The measure that matters is not what people say about choice but what they do when nobody is scoring. Nobody sets out to be governed by the sunk cost, yet it shapes an astonishing share of the ordinary day. Ask most people why they did what they did and they will give you a reason; ask them again a week later and the reason will have quietly changed.
The cost of being right
The usual story is that we are careless calculators. The better story is that we are careful about the wrong things. The remedy is rarely exhortation. It is a change to the situation so that the easier choice is also the better one. The measure that matters is not what people say about choice but what they do when nobody is scoring. The lesson is modest. Build for the person who exists, not the one in the model.
