CLARA: I know it's scary and difficult, but do you love being the man making the impossible choice?

DOCTOR: Why would I?

CLARA: Because it's what you do, all day, every day.

DOCTOR: It's my life.

CLARA: Doesn't have to be. Is it like-

DOCTOR: Like what?

CLARA: An addiction?

DOCTOR: You can't really tell if something's an addiction till you try and give it up.

CLARA: And you never have.

DOCTOR: Let me know how it goes.