If you are lucky, at some point in your life you will have the opportunity to witness a master at work--Bill Clinton wooing a crowd, LeBron James dunking, Yo-Yo Ma at the cello. DJ Khaled, 40, has Snapchat, the fast-growing social-messaging app. Khaled sends out missives--sometimes dozens--daily, locking his gaze into the front-facing camera of his iPhone and murmuring to his acolytes, who number in the millions. In these short bursts of footage, he provides a mix of confession and sermon. Right now he's filming himself while his beard is being blow-dried by a barber. "Fresh cut," he says into his phone, referring to the new haircut. He hits Send. Over the next 24 hours, the clip will be viewed by as many as 6 million fans.
Fame is ephemeral,…