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All I need to know, I learned by watching Dr. Who

"I've done so much. Saved entire races whose names I can't even remember. And why? Because of reasons. Because of principles. Truth, love, and harmony. Peace and goodwill. The best of intentions. Whatever I've done, I've done for these reasons. And there's been a price to pay. Sacrifices. People close to me have died. Four of my companions, hundreds of the universe's supporting cast. I could fill whole volumes with their names. Bystanders who helped me, perhaps for just a moment or two, and suffered for it. I've died myself, six times over. I have a responsibility. To every one of them, the living as well as the dead."
– The Seventh Doctor