When playing cards the dealer often offers you the possibility of cutting the deck into two parts and putting the top part to the bottom of the deck. Assume you can cut the deck not at a random position but at a fixed place, say you can grab exactly the first 20 cards. (This is not impossible, many professional "magicians" develop such skills.) People dont expect that one can do that and there is a question whether there is anything unfair if you use your (secret) skill