The lesson is modest. Build for the person who exists, not the one in the model. Nobody sets out to be governed by the commute, yet it shapes an astonishing share of the ordinary day. Put a number on fairness and it becomes a target; put a target on it and the number stops meaning what it meant. The point is not that people are foolish. The point is that fairness is expensive, and we economise on it like everything else.
Where the model breaks
The textbook treats fairness as a preference to be revealed. In practice it is a story we tell ourselves after the fact. The point is not that people are foolish. The point is that fairness is expensive, and we economise on it like everything else. Put a number on fairness and it becomes a target; put a target on it and the number stops meaning what it meant. Consider the commute. It is a small thing, and small things are where habits live.
