The honest conclusion is uncomfortable for reformers: people are not waiting to be corrected. We describe the departure from the model as an error. We might equally describe the model as a hopeful guess about us. 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. Put a number on risk and it becomes a target; put a target on it and the number stops meaning what it meant.
The ordinary case
Consider the borrowed book. It is a small thing, and small things are where habits live. The strange thing about the borrowed book is not that it exists but that it works, most of the time, for most people. The evidence here is thinner than the confident commentary suggests, and the honest position is a shrug with a direction of travel. None of this is new. Adam Smith noticed most of it, and then the profession spent two centuries forgetting.
It is tempting to call this irrational. It is more useful to ask what it is for. A pattern this consistent is not a character flaw. It is a design feature, and design features can be worked with. The mind that evolved for small groups and immediate dangers is now asked to manage a pension. It does its best. The usual story is that we are careless calculators. The better story is that we are careful about the wrong things.
