in The Imaginarium of Doctor Parnassus, Parnassus makes several deals or wagers with Mr. Nick, who is supposed to be a personification of the devil. However, we learn that most of the deals made with Mr. Nick, even when won, usually don't have a good ending.
For example, Parnassus became immortal and young again after a deal with Mr. Nick; however, in exchange he had to hand over any kids he had at the age of 16. So, while the deal may seem good to begin with, it still had a bad result.
And yet, Parnassus never learns to not take these deals. Why?