A few times, I have felt myself in the presence of true evil. At those times, I learned what it means to have the hair on the back of your neck stand up. It's not just an expression. It happened to me when I met with a leader who recruited cannon fodder for his "jihad," and on a few other occasions in the last couple decades that I've spent interviewing terrorists to learn why they do what they do. But, more often, the evil I've witnessed has been banal. I have found myself able to understand the mistaken moral logic that can turn a boy into a terrorist.