Sometimes known as alternative history. For Example, Winston Churchill was visiting Chicago in the early thirties when a taxicab knocked him down, he was shaken up but otherwise ok. It turned out that the cab had just come from a garage where the brake shoes had been replaced as the driver had been compaining it was not pulling up properly. If the brakes had not been fixed, Winny may have died and we would have lost a great war leader. Would it have made a diiference? You get the idea.