Proof of Fundamental Theorem of Poker?

[RustyBrooks]

I don't know of a "proof" of the theory but I think it is obvious to pretty much any poker player that you could not do better against an opponent than if you could see his cards, and he could not see yours (well, you could gain an improvement if you knew which cards were coming). Therefore, any time you take the same action you would have taken if you knew his cards, you took the best option possible.