Hardly anyone wants to be fat, after all, yet two-thirds of us are. A large proportion of smokers have tried to quit. Most procrastinators would prefer to escape their dilatory impulses but struggle to overcome their powerful wish to avoid work. The problem is that short-term rewards are just so much more seductive than long-term goals. People often understand how weak they are in this way, which is why (for example) they support the Social Security system, a giant precommitment device whereby we subject ourselves to taxation in order to forestall destitution that we could easily prevent if only we could save for ourselves.