It is an essential part of the scientific enterprise to admit ignorance, even to exult in ignorance as a challenge to future conquests. As my friend Matt Ridley has written, 'Most scientists are bored by what they have already discovered. It is ignorance that drives them on.' Mystics exult in mystery and want it to stay mysterious. Scientists exult in mystery for a different reason: it gives them something to do. More generally, as I shall repeat in Chapter 8, one of the truly bad effects of religion is that it teaches us that it is a virtue to be satisfied with not understanding.