Here’s what happens:

The spectator uses his or her own deck of cards. No set-up; it doesn’t even have to be a full deck. And, the performer never has to see the cards! Using a packet of ten random cards, the person selects one. Several cards are now discarded, so that the performer doesn’t even know how many cards are being used! Nevertheless, the spectator starts to deal down into the packet, and suddenly the performer knows that they are holding their selected card—and they are!