This is an effect Hofzinser created. You can read three versions of the original in Hofzinser's Card Conjuring. Three spectators choose two cards each and are asked to remember them both. Then they are asked to forget one of their cards. All six cards are returned and lost in the deck. Then spectator by spectator the performer finds the card the spectator remembered, shows it and places it face down on the table. As a climax those three remembered cards turn into the cards the spectators tried to forget.