The wartime prime minister's dark moods, plus a series of lucky encounters, may have transformed the course of human history, writes John Gray. Towards the end of his long life, when he was staying in a house lent to him by friends in the south of France, Winston Churchill sent for a young man who was helping him write one of the books with which he occupied his retirement. Churchill needed the young man as a researcher. But he also valued him as a companion, particularly in the evenings when he would otherwise feel lonely. One cold night they were sitting before the fire, where pine logs were hissing and spitting as they were burnt away. Churchill watched the blaze in silence. Then he growled: "I know why logs spit. I know what it is to be consumed." Churchill had not one life but several. Each was full of challenge and excitement, and in one of them he changed the history of the world. BBC News - A Point of View: Churchill, chance and the 'black dog'