DOCTOR: Isn't it obvious? The results of your meddling. Oh, do you never learn!?

NUN: Well, not really, no.

ANYA: You sure you don’t want to go and try your own people?

DOCTOR: Oh I want to go there more than you can imagine. Stand again under an orange sky, see the sun rising over the capitols… Oh I was so happy to see one of my own people again, even for a short while, but it’s gone. For me, all gone. I can’t go back, it would hurt too much. Just remind me of what I’ve lost.

ANYA: Not even for an hour?

DOCTOR: No, not even that. I’d be too tempted to change it and I can’t risk changing it. What’s going to happen has to happen. That’s just the way things are.