Rule No 1: The Client is Always Right!

We've all heard the old clich?©:
Rule No 1:The client is always right
Rule No 2:If the client is wrong, refer to Rule No 1.
This has always sounded a little prostitutive to me. (Yes, I know that there is no such word but I'm searching for an adjective associated with "prostitution.") What happens when the client really is wrong? Isn't it a bit trite to simply say: "Refer to Rule 1?"
Of course it is. Ross Holman (quoting Seth Godin) blogs about this today on his blog Strategize, prompting the thought. If the client is wrong, then they should not be the client any longer. Not for a moment longer than necessary, that is. How many clients do you have right now that, quite simply, are wrong? How much effort and emotional have you expended on trying to make things right, only to find out that you can't? Imagine how much time you might have saved if you had simply fired that client, and the benefits that would have accrued if all that effort had been expended on more worthwhile clients instead.
Comments, as always, are most welcome and may be posted below.