"I've made sacrifices! You don't know what it cost me to climb into that machine every night, not knowing if I'd be the man in the box or in the prestige!"

You know, I never could make sense out of that line. If you assume the machine creates "copies" (and that's strongly implied by the story up to that point), then that means every time he gets on stage, he's going to wind up in the box. (And even if the copies are error-free and absolutely interchangeable, one copy will still end up in the box.)

(Edit to add: of course, if you view it from the quantum suicide POV, "he" never ends up in the box, since otherwise "he" would not be there to try again the next night.)