When Philip K. Dick wrote "The Man In The High Castle" in 1962, he left many of his major plot points to chance. Dick would throw coins and, using the ancient Chinese divination text the I Ching, let the characters' actions be dictated to him. "That governed the direction of the book," he said later. "Like in the end when Juliana Frink is deciding whether or not to [do a big thing], the answer indicated that she should. Now if it had said not to, I would have had her not go there."
The risk, of course, is that the coins will lead you somewhere boring.