Why Do Clients Think This Way?

The Client-Agency relationship has always baffled me. When I started in advertising, I was taught that the best relationship between Client and Agency is one of partnership -- The Agency cares about hte Client's business so he helps it to grow, at the same time, the Client helps the Agency to grow as a business. Mutually-beneficial. And so, we at the Agency always strive to bring out the best in this relationship, protect it to death and make some concessions along the way.

But it doesn't work out that way a lot of times. Despite the value the Agency brings to the Client, some Clients take the relationship and turn it around to pull a fast one on the Agency. All because they're the ones holding the money and will get away with it if they can.

Check this video out, purportedly created by Leo Burnett according to Nadja, and see the similarities with how clients negotiate payment for services they've already received or are about to receive:

Why do some clients think this way? Is it because they don't have scrupules to begin with? Is it because they're stupid enough to think this way? Or is it because we let them get away with it?

I'd like to know what you think. Meanwhile, I need to rush to another client meeting. :P