Teller, the silent half of the Penn & Teller magic act, explains seven cognitive biases that magicians exploit in order to "alter the perceptions" of their audiences and achieve impossible-seeming feats.
The "tricks" are to: exploit pattern recognition (do two things that seem similar and we'll assume they're the same thing); make the secret a lot more trouble than it seems worth (we'll discount the possibility that a trivial effect was the result of years of work); make 'em laugh (jokes distract you from thinking through the trick); do the trick outside the frame (we assume the trick is the part that seems showy, not mundane things like shedding a jacked "before the trick starts"); make you lie to yourself (let the audience glimpse a "mistake" that reveals a false explanation for the trick); and create the illusion of free choice (we assume that choices are freely made).
To explain how these work, Teller gives the example of letting you choose a card from a deck, then seeming to chew on the deck, digesting one card and moving it to his shoe, and "forgetting" the deck so you can verify that your card's missing from it.
THE SECRET(S) First, the preparation: I slip a queen of hearts in my right shoe, an ace of spades in my left and a three of clubs in my wallet. Then I manufacture an entire deck out of duplicates of those three cards. That takes 18 decks, which is costly and tedious (No. 2—More trouble than it’s worth).
When I cut the cards, I let you glimpse a few different faces. You conclude the deck contains 52 different cards (No. 1—Pattern recognition). You think you’ve made a choice, just as when you choose between two candidates preselected by entrenched political parties (No. 7—Choice is not freedom).
Now I wiggle the card to my shoe (No. 3—If you’re laughing...). When I lift whichever foot has your card, or invite you to take my wallet from my back pocket, I turn away (No. 4—Outside the frame) and swap the deck for a normal one from which I’d removed all three possible selections (No. 5—Combine two tricks). Then I set the deck down to tempt you to examine it later and notice your card missing (No. 6—The lie you tell yourself).
Teller Reveals His Secrets