Institutions know all this, of course, which is why the shortcut is so rarely left to chance. 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. 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 habit but what they do when nobody is scoring.
What follows
If you want to see habit at work, watch a queue form where there is no reason for one. The lesson is modest. Build for the person who exists, not the one in the model. The mind that evolved for small groups and immediate dangers is now asked to manage a pension. It does its best. The strange thing about the shortcut is not that it exists but that it works, most of the time, for most people.
What looks like habit from the outside is usually something simpler from the inside: tiredness, a deadline, a wish not to look foolish. Understanding people turns out to be a more urgent task than changing them, and a great deal harder. The lesson is modest. Build for the person who exists, not the one in the model. The point is not that people are foolish. The point is that habit is expensive, and we economise on it like everything else.
