There are certain people in whom you can detect the seeds of madness - seeds that have remained dormant only because the people in question have lived relatively comfortable, middle class lives. They function perfectly well in the world, but you can imagine, given a nasty parent, or a prolonged bout of unemployment, how their potential for craziness might have been realized.
Notes on a Scandal (ed. Penguin UK, 2007) - ISBN: 9780141901916