A boy was in an empty room and went to a holy man at the front. He said to the boy, "If I write your exact weight on a piece of paper then you have to give me $50, but if I cannot, I will pay you $50."
The boy looked around and saw no scale so he agrees, thinking no matter what the man writes he'll just say he weighs more or less.
In the end the boy ended up paying the man $50. How did the man win the bet?