Somebody you know once turned their life around. Ask what changed first. It wasn't the habits, and it wasn't willpower. They changed their answer to one question: who am I?

It begins with five hundred boys from the reform schools of Boston, picked out in 1940 and followed through the records to the age of seventy. The ones who got out of crime did not do it by gritting their teeth. A marriage that lasted, a stretch in the army, a job that held: something handed them a new sense of who they were, and the habits followed the man.

Then a way to see it. A hotel cleaner's ring: a guest key opens one room, and one belief is one room. A floor key opens every room on a floor with one turn, which is what it means to be something: hand a person the key marked runner and thirty beliefs open at once. And the master key opens everything. In a pers ...