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.
Zoë Heller, What Was She Thinking? [Notes on a Scandal]
insanity