Fear as described in "The Life of Pi" by Yann Martel

"I must say a word about fear. It is life's only true opponent. Only fear can defeat life. It is a clever, treacherous adversary... It has no decency, respects no law or convention, shows no mercy. It goes for your weakest spot, which it finds with unerring ease. It begins in your mind, always. One moment you are feeling calm, self-possessed, happy. Then fear, disguished in the garb of mild-mannered doubt, slips into your mind like a spy. Doubt meets disbelief and disbelief tries to push it out. But disbelief is a poorly armed foot soldier. Doubt does away with it with little trouble. "