One of my favorite quotes is from Sun Tzu's Art of War and readapted by Orson Scott Card. When Ross was talking about having to know yourself before one could defeat the evil in yourself.
"In the moment when I truly understand my enemy, understand him well enough to defeat him, then in that very moment I also love him. I think it’s impossible to really understand somebody, what they want, what they believe, and not love them the way they love themselves. And then, in that very moment when I love them.... I destroy them."
This is one of my favorite quotes about war and strategy for the reason that it takes 'you have to think like the enemy' to an entirely new level, and also touches on the fact that if we are to defeat our enemies, we must understand them so much that we love them, which in turn makes us not want to destroy them. This thought in war has always fascinated me.