Doctor: You can spend the rest of your life with me. But I can't spend the rest of mine with you. I have to live on. Alone. That's the curse of the Time Lords.
Sarah-Jane: I had no problem with space stuff. I saw things you wouldn't believe.
Rose: Try me.
Sarah-Jane: Mummies.
Rose: I've met ghosts.
Sarah-Jane: Robots. Lots of robots.
Rose: Slitheen. In Downing Street.
Sarah-Jane: Daleks!
Rose: Met the Emperor.
Sarah-Jane: Anti-Matter monsters.
Rose: Gas masked zombies.
Sarah-Jane: Real living dinosaurs!
Rose: Real living werewolf!
Sarah-Jane: The Loch Ness Monster!
Rose: Seriously?
Chosen answer: The Master knows that deep down, he deserves death for the crimes that he's committed throughout his life, and since he regards The Doctor as his arch-foe, he expects it to be at his hands. The fact that The Doctor is still willing to forgive him for all of his crimes hurts him more deeply than death would.
Captain Defenestrator