Think of a card, and then you can find out the magic of poker.

Prepare 2 1 card first, divide it into three parts, ask if it is in it, put the card they have in the middle, reissue it, repeat it three times, and ask for it for the last time. The card he chose is right in the middle of this point. Principle is the basic reasoning in higher mathematics. You don't have to worry, just remember this. And it can be combined with other magic, and the effect is better.