" If you define madness as the opposite of sane, you are forced into providing a definition of sanity. Can you define it? Can you tell me what it is to be sane? Is it to hold no beliefs that are contrary to reality? That our thoughts and actions contain no absurd contradictions?...If that is your criterion, then we are all mad—except those of us who make no claim to understand the difference. Perhaps there is no difference, except in our own heads. In other words...madness is a wholly human malady borne in a brain too evolved—or not quite evolved enough—to bear the awful burden of its own existence. "

― Rick Yancey , The Final Descent (The Monstrumologist, #4)