Every one of us runs the same shortcut, and every one of us believes we are the exception. The strange thing about the borrowed book is not that it exists but that it works, most of the time, for most people. The textbook treats trust as a preference to be revealed. In practice it is a story we tell ourselves after the fact. The point is not that people are foolish. The point is that trust is expensive, and we economise on it like everything else.
Three kinds of mistake
Notice how rarely anyone is argued out of the borrowed book, and how often they are simply moved past it by a change in circumstance. The measure that matters is not what people say about trust but what they do when nobody is scoring. Economists have spent decades modelling trust as a quantity. It behaves more like a weather system. The textbook treats trust as a preference to be revealed. In practice it is a story we tell ourselves after the fact.
Institutions know all this, of course, which is why the borrowed book is so rarely left to chance. The point is not that people are foolish. The point is that trust is expensive, and we economise on it like everything else. The evidence here is thinner than the confident commentary suggests, and the honest position is a shrug with a direction of travel. The mind that evolved for small groups and immediate dangers is now asked to manage a pension. It does its best.
