We have choices in life, and often these choices 
effect the outcome of certain events. What card you play or do not play can cause your opponents to make choices that can be in your favor. False-carding is playing a card you would not normally play - but will not cost anything - and can snare your opponents into making the wrong decision. Some counter intuitive action is usually involved. Here is a typical example of false-carding. Contract is 4 S, in example 1, on the right. 
        North  leads the A H. The defenders are on the verge of taking two Hearts, the A S (always a winner) and the A u for down one. How can you stop North from leading the second Heart (K H)?  Spilling hot coffee on his lap might hurt enough for him to forget Hearts and switch to a Club. Nice try, but there is another way. On the opening lead of the A H you play the 2 H from Dummy; wait for your right hand opponent to  play a card; and then without  hesitation, no guilty looks, but very naturally table the Q H from your hand. This Q H is a false-card. You would normally play the 8 H. This little piece of dissembling gives the impression that the Q H is a singleton; that you will trump the next Heart lead. Also note that this play is a freebee, it costs the Declarer nothing. Now West starts to think. (Could be a dangerous activity for some and  painful for others.) What good player in his or her right mind, and there are a few, would now lead the K H? It will get trumped by Declarer and the J H in Dummy will now become a winner. 
        At trick two North switches to a Club. Win the K C in your hand and play the 7 C to Dummy's Ace. Now for the coup de false-card. Play the Q C and dump your Heart loser (8 H). The final results: you lost a Heart (A H) at trick one; you will lose the Ace of trumps ( A S); and the A u. You lost just three tricks, made 10 and made your contract of 4 S. What have we learned from this hand? One - never give up. Two - expect the unexpected. Three - think and stratagize before playing the first card. And four - never miss an opportunity to  swindle your opponents.


       S  Q 8 7 6         H  J 5 2 
       D  Q 8 7 
       C  A Q 4

     S  K J 10 5 4 3
     H  Q 8
  D  K 9 2
     C   K 7