A boy was at a carnival and went to a booth where a man said to the boy, “if I write your exact weight on this piece of paper, 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 agreed, thinking that no matter what was written, he could say more or less. In the end, the boy ended up paying the man $50.
How did the man win the bet?