If you want to deter crime, it seems that you’d want to lengthen prison sentences so that criminals would face steeper costs for breaking the law. In fact, a mountain of research shows that increases in prison terms have done nothing to deter crime. Criminals, like the rest of us, aren’t much influenced by things they might have to experience far in the future.

If a police officer witnesses the death of his partner, it seems that you’d want to quickly send in a grief counselor. In fact, this sort of immediate counseling freezes and fortifies memories of the trauma, making the aftershocks more damaging.

If you want to get people to vote more, it seems you’d want to tell them what a problem low turnout is. In fact, if you want people to vote, tell them everybody else is already voting and they should join the club. Voting is mostly about social membership and personal expression.

These are three examples of policies and practices that are based on bad psychology. The list of examples could go on and fill this page. That’s because we spend trillions of dollars putting policies and practices into place, but most of these efforts are based on the crudest possible psychological guesswork.