Leading Double Lives

Stories of those who lead double lives are both daring and baffling. What compels a person to attempt to become someone else? Is it merely for material gain, to pull off an ingenious scam? Or is there a deeper reason? At one time or another, we've all fantasized about trying on a new identity, but when does the line between impersonation and transformation get blurred? Is it possible that by pretending to be someone else, a person can actually become that person, at least in their mind?