There are a lot of bar­ri­ers to chang­ing your mind: ego, over­con­fi­dence, iner­tia — and cost. Politi­cians who flip-flop get mocked; fam­i­ly and friends who cross trib­al bor­ders are shunned. But shouldn’t we be encour­ag­ing peo­ple to change their minds? And how can we get bet­ter at it ourselves?