You don't think I know what pain is? How it never goes away? [Oh and that's real disbelief in his voice, real anger as he steps forward.] I know first-hand that fire's not a joke, Zuko. Fire destroyed my village. My family. FIRE did that. But you know what? It taught me a lesson, too. You have to fight for the people you care about. Your friends. You have to keep fighting because a home isn't important if you don't have anyone there with you.

You. Are. My. Friend. [He actually pokes Zuko in the chest with each of the words.] So if it takes getting burned to make you remember that, then go ahead. It's a pain I'm willing to live with.