That's what Ender has to understand. There really is evil in the world, and wickedness, and every brand of stupidity. There's meanness and heartlessness and... I don't even know which of them is me." - Hyrum Graff

Ender Wiggin isn't a killer. He just wins—thoroughly.

You get all the pleasures of the puppeteer.

Graff had isolated Ender to make him struggle. To make him prove, not that he was competent, but that he was far better than everyone else. That was the only way he could win respect and friendship. It made him a better soldier then he would ever have been otherwise. It also made him lonely, afraid, angry, untrusting. And maybe those traits, too, made him a better soldier.

Keep this in mind - it only works because what's between you, that's real, that's what matters. Billions of those connections between human beings. That's what you're fighting to keep alive.

When you walk on the face of a world, then forgiveness comes.