The Prestige is an allegory for filmmaking. The entire point of the thing is asking the question of how far or how many sacrifices one will make to pursue the excellence of the craft (embodied by the fishbowl story. To sell the act, the Chinese man had to live the role. The twins had to live as one person, giving up half of themselves to do so). Remember, we all know going into a film (or magic act) that it is not real. Yet, the best filmmakers and actors are constantly able to get us to suspend disbelief by totally embodying the role. This is the very concept that consumed Ledger. Definitely my favorite Nolan joint.