RIVER: You have no idea, do you? What you mean to them?

DOCTOR: Me? I’m just passing through, I give people rides, they have fun for the most part when they’re not being captured, shot at, or blown up. But sometimes, sometimes it gets real. I find something that’s too big, too dangerous. And I care about them. I can’t risk their lives. Not them

RIVER: You love them too!

DOCTOR: I can’t afford to let people get attached.

RIVER: It’s lucky I’m here then. As an impartial observer.