My neighbor owes me $500 and he won't pay up

My neighbor owes me $500 and he won't pay up

A man went to his lawyer and told him, ‘My neighbour owes me $500 and he won’t pay up. What should I do?’
‘Do you have any proof he owes you the money?’ asked the lawyer.
‘Nope,’ replied the man.
‘OK, then write him a letter asking him for the $1,000 he owed you,’ said the lawyer.
‘But it’s only $500,’ replied the man.
‘Precisely. That’s what he will reply and then you’ll have your Proof!’