The fundamental theorem of poker states: Every time you play your hand the way you would if you could see your opponents' cards, you gain, and every time your opponents play their cards differently from the way they would play them if they could see your cards, you gain. This theorem is the foundation for many poker strategy topics. For example, bluffing and slow-playing are examples of using deception to induce your opponents to play differently from how they would if they could see your cards. There are some exceptions to the fundamental theorem in certain multi-way pot situations.

See Post for Morton's Theorem.