...And that's surely what it boils down to. I've said it already, no one is able to keep on going with the Doctor forever. Five years ago I probably wouldn't have given it a second thought and hopped on in. Now I'm married with a kid and leaving them would never occur to me, as awesome as seeing the universe would be. And I'm sure the Doctor wouldn't want me changing diapers in a smelly corner of the console room. Mark
I bet in reality it'd be scary as hell though. I don't know that I'd be of stern enough stuff to do it.