The anthropologists got it wrong when they named our species Homo sapiens ('wise man'). In any case it's an arrogant and bigheaded thing to say, wisdom being one of our least evident features. In reality, we are Pan narrans, the storytelling chimpanzee.

People think that stories are shaped by people. In fact, it's the other way around.

Down there - he said - are people who will follow any dragon, worship any god, ignore any inequity. All out of a kind of humdrum, everyday badness. Not the really high, creative loathsomeness of the great sinners, but a sort of mass-produced darkness of the soul. Sin, you might say, without a trace of originality. They accept evil not because they say yes, but because they don't say no.

Inside every sane person there's a madman struggling to get out," said the shopkeeper. "That's what I've always thought. No one goes mad quicker than a totally sane person.

Oh. I see. People don't want to see what can't possibly exist.

But there was more to it than that. As the Amazing Maurice said, it was just a story about people and rats. And the difficult part of it was deciding who the people were, and who were the rats.