Harry Potter and the Methods of Rationality

Harry stared up at the gray ceiling of the small room, from where he lay on the portable yet soft bed that had been placed there. He'd eaten quite a lot of Professor Quirrell's snacks - intricate confections of chocolate and other substances, dusted with sparkling sprinkles and jeweled with tiny sugar gems, looking highly expensive and proving, in fact, to be quite tasty. Harry hadn't felt the least bit guilty about it either, this he had earned.

He hadn't tried to sleep. Harry had a feeling that he wouldn't like what happened when he closed his eyes.

He hadn't tried to read. He wouldn't have been able to focus.

Funny how Harry's brain just seemed to keep on running and running, never shutting down no matter how tired it got. It got stupider but it refused to switch off.

But there was, there really and truly was a feeling of triumph.

Anti-Dark-Lord-Harry program, +1 point didn't begin to cover it. Harry wondered what the Sorting Hat would say now, if he could put it on his head.

No wonder Professor Quirrell had accused Harry of heading down the path of a Dark Lord. Harry had been too slow on the uptake, he should have seen the parallel right away -

Understand that the Dark Lord did not win that day. His goal was to learn martial arts, and yet he left without a single lesson.

Harry had entered the Potions class with the intent to learn Potions. He'd left without a single lesson.

And Professor Quirrell had heard, and understood with frightening precision, and reached out and yanked Harry off that path, the path that led to his becoming a copy of You-Know-Who.

There was a knock at the door. "Classes are over," said Professor Quirrell's quiet voice.

Harry approached the door and found himself suddenly nervous. Then the tension diminished as he heard Professor Quirrell's footsteps moving away from the door.

What on Earth is that about? Is it what's going to get him fired eventually?

Harry opened the door, and saw that Professor Quirrell was now waiting several bodylengths away.

Does Professor Quirrell feel it too?

They walked across the now-deserted stage to Professor Quirrell's desk, which Professor Quirrell leaned on; and Harry, as before, stopped short of the dais.

"So," Professor Quirrell said. There was a friendly sense about him somehow, even though his face still kept its usual seriousness. "What was it you wanted to talk to me about, Mr. Potter?"

I have a mysterious dark side. But Harry couldn't just blurt it out like that.

"Professor Quirrell," Harry said, "am I off the path to becoming a Dark Lord, now?"

Professor Quirrell looked at Harry. "Mr. Potter," he said solemnly, with only a slight grin, "a word of advice. There is such a thing as a performance which is too perfect. Real people who have just been beaten and humiliated for fifteen minutes do not stand up and graciously forgive their enemies. It is the sort of thing you do when you're trying to convince everyone you're not Dark, not -"

"I can't believe this! You can't have every possible observation confirm your theory!"

"And that was a trifle too much indignation."

"What on Earth do I have to do to convince you?"

"To convince me that you harbor no ambitions of becoming a Dark Lord?" said Professor Quirrell, now looking outright amused. "I suppose you could just raise your right hand."

"What?" Harry said blankly. "But I can raise my right hand whether or not I -" Harry stopped, feeling rather stupid.

"Indeed," said Professor Quirrell. "You can just as easily do it either way. There is nothing you can do to convince me because I would know that was exactly what you were trying to do. And if we are to be even more precise, then while I suppose it is barely possible that perfectly good people exist even though I have never met one, it is nonetheless improbable that someone would be beaten for fifteen minutes and then stand up and feel a great surge of kindly forgiveness for his attackers. On the other hand it is less improbable that a young child would imagine this as the role to play in order to convince his teacher and classmates that he is not the next Dark Lord. The import of an act lies not in what that act resembles on the surface, Mr. Potter, but in the states of mind which make that act more or less probable."

Harry blinked. He'd just had the dichotomy between the representativeness heuristic and the Bayesian definition of evidence explained to him by a wizard.