The mind that evolved for small groups and immediate dangers is now asked to manage a pension. It does its best. The evidence here is thinner than the confident commentary suggests, and the honest position is a shrug with a direction of travel. Every one of us runs the same shortcut, and every one of us believes we are the exception. A pattern this consistent is not a character flaw. It is a design feature, and design features can be worked with.
What the evidence shows
Every one of us runs the same shortcut, and every one of us believes we are the exception. The textbook treats reason as a preference to be revealed. In practice it is a story we tell ourselves after the fact. Nobody sets out to be governed by the borrowed book, yet it shapes an astonishing share of the ordinary day. It is tempting to call this irrational. It is more useful to ask what it is for.
The lesson is modest. Build for the person who exists, not the one in the model. The measure that matters is not what people say about reason but what they do when nobody is scoring. It is tempting to call this irrational. It is more useful to ask what it is for. Institutions know all this, of course, which is why the borrowed book is so rarely left to chance.
