But at eight, 10, 12, you don't realise you're going to die. There is always the possibility of escape. There is always somewhere else and far away, a fact I had never really appreciated until I read Gitta Sereny's profoundly unsettling Cries Unheard about child-killer Mary Bell.
At 20, 25, 30, we begin to realise that the possibilities of escape are getting fewer. We begin to picture a time when there will no longer be somewhere else and far away. We have jobs, children, partners, debts, responsibilities. And if many of these things enrich our lives immeasurably, those shrinking limits are something we all have to come to terms with.
This, I think, is the part of us to which literary fiction speaks.
Genre fiction says: 'Forget the gas bill. Forget the office politics. Pretend you're a spy. Pretend you're a courtesan. Pretend you're the owner of a crumbling gothic mansion on this worryingly foggy promontory.' Literary fiction says: 'Bad luck. You're stuck with who you are, just as these people are stuck with who they are. But use your imagination and you'll see that even the most narrow, humdrum lives are infinite in scope if you examine them with enough care.'

Mark Haddon, author of The Curious Incident of the Dog in the Night on writing for children, Jane Austen, religion, technology, and, oh, just go read it.