Steven Moffat, on casting Matt Smith.
River Song: You know when you see a photograph of someone you know, but it’s from years before you knew them. It’s like they’re not quite finished; they’re not done yet. Well, yes, the Doctor’s here. He came when I called just like he always does, but not “my” Doctor. Now my Doctor, I’ve seen whole armies turn and run away, and he’d just swagger off back to his TARDIS and open the doors with a snap of his fingers. The Doctor in the TARDIS. Next stop: Everywhere.
“And I can always see you.”
“Then why didn’t you speak to me?”
“Because I thought it would hurt too much.”
“I believe I could have coped.”
“No. I thought it would hurt me. And I was right.”