Economists have spent decades modelling loyalty as a quantity. It behaves more like a weather system. None of this is new. Adam Smith noticed most of it, and then the profession spent two centuries forgetting. 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. A better account of loyalty would begin with the ordinary case rather than the laboratory one.
What follows
Consider the receipt. It is a small thing, and small things are where habits live. The usual story is that we are careless calculators. The better story is that we are careful about the wrong things. 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. Notice how rarely anyone is argued out of the receipt, and how often they are simply moved past it by a change in circumstance.
