currently reading "The Kite Runner" with a high school freshman class and writing Haiku as an exercise in poetry forms. This fell out in a moment of concentration while they were writing their own.  The title is from a Nietzschean aphorism admonishing against fighting monsters lest you become what they are.
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - F. Nietzsche