DOCTOR: Amazing thing, history. People always assume it's a straight line because they're in the middle of it. Viewed from outside it's more like a Möbius strip.

I’ve been too methodical recently, I think. Setting coordinates and things, actually deciding where we want to go. I’ve been getting far too safe and predictable these last few incarnations. Do you know I once traveled for centuries without ever knowing where I’d materialize next?

DOCTOR: But it was a childish dream that made you a doctor! You dreamt you could hold back death. Isn't that true? Don't be sad, Grace. You'll do great things.