To be transferred to a single person, a meme need seem useful only to that person. To be transferred to a group of similar people under unchanging circumstances, it need be only a parochial truth. But what sort of idea is best suited to getting itself adopted many times in succession by many people who have diverse, unpredictable objectives? A true idea is a good candidate. But not just any truth will do. It must seem useful to all those people, for it is they who will be choosing whether to enact it or not.
