A man went to his lawyer and told him, "My neighbour owes me $500 and
he doesn't want to pay up. What should I do?"

"Do you have any proof?", asked the lawyer. "Nope," replied the man.

"Okay, then write him a letter asking him for the $1,000 he owes you,"
said the lawyer.

"But it's only $500!" replied the man.

"Precisely, that's what he will reply and we will have the proof we
need," said the lawyer.