You Control the Outcome.
Its a 50 / 50 Chance or IS IT? Win or Lose!
Show three keys, only one opens the lock. Make a wager, mix the keys, two spectators select a key for themselves, the remaining key is yours. They can trade their key for your key, but it doesn't matter! They BOTH insert their key into the lock, it does NOT unlock the lock!
You insert your key, it UNLOCKS the lock! Many, Many routines are now possible with the Win or Lose Lock.