Mor

“I consider that a man's brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things, so that he has a difficulty in laying his hands upon it. Now the skillful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work, but of these he has a large assortment, and all in the most perfect order. It is a mistake to think that that little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.”
― Arthur Conan Doyle, A Study in Scarlet

“[The Doctor, Capt. Jack and Rose are cornered by the empty children.]
The Doctor: Go to your room! Go to your room! I mean it. I'm very, very angry with you. I'm very, very cross! GO! TO! YOUR! ROOM! [The children lurch away and obey him.] I'm really glad that worked. Those would have been terrible last words.”
― Steven Moffat

“The Doctor: Just had a fall. All the way down there, right to the library. Heck of a climb back up.
Amelia: You're soaking wet.
The Doctor: I was in the swimming pool.
Amelia: You said you were in the library.
The Doctor: So was the swimming pool.”
― Steven Moffat

“When you run with the Doctor, it feels like it'll never end. But however hard you try you can't run forever. Everybody knows that everybody dies and nobody knows it like the Doctor. But I do think that all the skies of all the worlds might just turn dark if he ever for one moment, accepts it. Everybody knows that everybody dies. But not every day. Not today. Some days are special. Some days are so, so blessed. Some days, nobody dies at all. (In the library, the Doctor walks back to the TARDIS. He stops, looking at the doors. Then he raises his hand, and stands there poised like that for a long moment. Finally he snaps his fingers. The doors open. He smiles slowly and walks in, joining Donna. Then he snaps his fingers again, and the doors close. River's voice continues over this.) Now and then, every once in a very long while, every day in a million days, when the wind stands fair, and the Doctor comes to call... everybody lives.”
― Steven Moffat