The lesson is modest. Build for the person who exists, not the one in the model. 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 strange thing about the loyalty card is not that it exists but that it works, most of the time, for most people. In the studies we have, the effect is modest, reliable and almost entirely ignored by the people it describes.
What it gets right
The evidence here is thinner than the confident commentary suggests, and the honest position is a shrug with a direction of travel. The lesson is modest. Build for the person who exists, not the one in the model. Institutions know all this, of course, which is why the loyalty card is so rarely left to chance. The mind that evolved for small groups and immediate dangers is now asked to manage a pension. It does its best.
