I used to be convinced that my wallet—a simple fold-up piece that fit neatly in my must have hand bag—was actually a prop in some magician’s disappearing act. Cash seemed to vanish from it the moment I left the ATM. Crisp twenty-dollar bills were replaced with worn out ones and fives. I was baffled: was there a secret pocket? A trick flap? Where was all of my money going? To my dismay I was responsible. I was spending it of course—but in such a way that I never realized how quickly it all added up, or subtracted.