There is a superstition surrounding the number 23. It is said that actively trying to avoid the number only makes the connection more likely.
The spectator is told he will intentionally select a lucky card and use the number associated with that card. He is invited to cut off less than half the deck and to shuffle the cut-off cards. He is told to fan the cards in front of himself and remember any card number card he sees.
The spectator turns the fan of cards face down again and shuffle them so even he has no idea which of the cards is the one he mentally selected.

“This deck has 52 cards but you are going to intentionally upset the 23 Enigma by hiding some of the cards. Silently remove a group of cards equal to whatever card you mentally chose. For example, if you are thinking of the Ten of Spades, silently remove any ten cards and hide them in the card case then place any remaining cards back onto the rest of the deck.”

The performer suggests that the Enigma occurs no matter what you do to try to avoid it. After counting down exactly 22 cards in the pack he reveals that the 23rd card is not only the only red-backed card in the deck but that it also has a giant number 23 printed on it.

Without ever speaking the name of his card, the spectator turns over the red back card to discover that it is exactly the same as his mentally selected card.