There's a "card trick" magicians often like to do which is to simply ask the spectator to name a card at random. If they, by pure chance, happen to name the card that the performer already knows is on top of their deck of cards (eg because they peeked at it), then they reveal the card and it looks like they performed an impossible trick. If they named any other card, then the performer simply does another trick (perhaps looping back to the named card later or perhaps simply ignoring it or making a joke). Its a good opener: if it works, it grabs everyone's attention for the remainder of the act and if it fails, nobody will even notice as they get distracted by the actual routines.

Every so often, pure random chance means that they get it right and it looks incredible to the spectators who witness it.