There is a version of this essay that ends with a policy prescription. This is not that version; the mechanism is interesting enough on its own. It is tempting to call this irrational. It is more useful to ask what it is for. Notice how rarely anyone is argued out of the weather forecast, and how often they are simply moved past it by a change in circumstance. The lesson is modest. Build for the person who exists, not the one in the model.
Three kinds of mistake
It is tempting to call this irrational. It is more useful to ask what it is for. The remedy is rarely exhortation. It is a change to the situation so that the easier choice is also the better one. The point is not that people are foolish. The point is that trust is expensive, and we economise on it like everything else. Understanding people turns out to be a more urgent task than changing them, and a great deal harder.
