Economic models are simplifications. As in Jorge Luis Borges’s parable of a map that grew to be the same size as the empire it charted, there is no purpose in a model that captures all of the messy complexity of reality. Models are helpful because they leave things out. And patterns of irrational behavior are often dismissed as insignificant variations. Economists didn’t think people actually spent windfalls on exactly the things they wanted most. But they regarded the reality as close enough.