"Belief in the inevitable always presupposes a sort of vacuum in which forces are working. The moves in a game of chess are mathematical facts, but suppose you prophesy that one player in a certain game will checkmate his opponent in a number of moves. He may go crazy, or kick over the board in rage, or in a spirit of compassion make all his moves the wrong ones. All predictions are like that. They presuppose that the rules will be kept to, but suppose they are not?"
-Gilbert Keith Chesterton, as excerpted from here