I would agree that it is the correct response. It sounds stupid to just let people get one over on you, sure. But every freelancer (that I know of) has been screwed by a client at some point.

Since it happens to everyone, the interesting part of the story becomes how you handled it. Not that it happened.

Fact: he is already convinced that he's better off, because he is. Read his post again.

IMHO these aren't "mental tricks" but valid suggestions for him to find closure to something from the past that he really shouldn't consider important anymore. Finding peace is good.

A few people in this thread are saying to let it go, to write it off. My post gives a technique that can be used to do that effectively.

The correct response is to try to recoup your losses, but, not lose too much sleep over them, because I guarantee they are not losing any sleep over you.

Much as with anyone who screws you over, or otherwise causes you problems.