The Mystic Seven

Effect: You predict which pile of cards a spectator will choose.
Secret: One a piece of paper, you write: "You will choose the Seven pile". The paper is then folded and given to a spectator for safekeeping. You now take several cards from a pack and arrange them in three facedown piles. The three piles are formed as follows: Pile One: Any seven cards. Pile Two: The four Sevens. Pile Three: An Ace, a Two and a Four (which add up to seven). A spectator is given the choice of any of the three piles. Whichever pile is chosen the prediction is always correct.