The Doctor squeezed his eyes shut at Jack's admittance. He remembered the man who killed him. Just a blurry face in a dark sewer, but he remembered. The utter heartlessness in it should've infuriated the Doctor, but it just made him sad. There were people like that all over the universe, no matter what anyone did. No matter what Jack tried to do to stop it.

"Revenge---"

He opened his eyes and turned to look at Jack, sad and serious. "Revenge doesn't solve anything, Jack. Nothing at all."