There exists a basic Law of Human Nature, and we all understand it exists.
Recently, the CBS TV Show Survivor featured Russell, a particularly aggressive player whose strategy was to create chaos between other players that only he could come in and solve. He openly lied and broke the rules of fair play, but the other players never caught on that they were being manipulated – until the very last episode when he admitted proudly that this was his strategy and that his actions proved his strategy was the best and that he ought to win the game.
Every contestant on the show knew then that this man had broken the Law of Human Nature and had played unfairly. When the voting for the winning Survivor came about, it was a different player who was selected by the players as the best. Natalie White got to the finalists by playing more closely to the Rule of Fair Play than the villainous contestant.
In the end, the game show contestants could not reward someone who so blatantly played outside the Rule of Fair Play. Mind you, the game itself had no rules except to get someone else voted out instead of yourself. By the game's history, the villain should have won -- he certainly thought he had the victory in the bag. But by the Rule of Fair Play that everyone sensed, most of the contestants who had stuck more closely with the Law of Fair Play while playing Survivor. Selfishness has never been admired.
This show is a modern example, I think, of C. S. Lewis' conclusion that there is a universal Law of Fair Play. It is as powerful as the instinct for self-preservation, but it differs from a "herd instinct" because there is a choice to be good or to be evil. In fact, truth be told, all of us have difficulty following the Law of Fair Play -- we frequently chose to do wrong -- maybe not as blatantly as Survivor's Russell, but we do find it hard to be perfect. Still, when we bread the code, we know it. Deep inside, we know it and we try to justify the bad behavior.