The Doctor: [lowers his voice] Because I can't see it anymore. I'm 907. After a while... you just can't see it!... I look at a star and it's just a big ball of burning gas and I know how it began and I know how it ends and I was probably there both times. After a while, everything is just stuff! That's the problem. You make all of space and time your backyard and what do you have? A backyard. But you, you can see it. And when you see it, I see it.