Institutions know all this, of course, which is why the borrowed book is so rarely left to chance. We describe the departure from the model as an error. We might equally describe the model as a hopeful guess about us. 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.
A better question
None of this is new. Adam Smith noticed most of it, and then the profession spent two centuries forgetting. 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. Every one of us runs the same shortcut, and every one of us believes we are the exception. A better account of nostalgia would begin with the ordinary case rather than the laboratory one.
