Every one of us runs the same shortcut, and every one of us believes we are the exception. Nobody sets out to be governed by the sunk cost, yet it shapes an astonishing share of the ordinary day. The point is not that people are foolish. The point is that habit is expensive, and we economise on it like everything else. The remedy is rarely exhortation. It is a change to the situation so that the easier choice is also the better one.
What the evidence shows
What looks like habit from the outside is usually something simpler from the inside: tiredness, a deadline, a wish not to look foolish. The textbook treats habit as a preference to be revealed. In practice it is a story we tell ourselves after the fact. Understanding people turns out to be a more urgent task than changing them, and a great deal harder. A better account of habit would begin with the ordinary case rather than the laboratory one.
