Harry Potter and the Methods of Rationality

"I wasn't going to," said the kindly voice of Hermione Granger. "It didn't seem nice."

"Just get it over with," said Harry.

"Okay! So you gave me this whole long lecture about how hard it was to do basic science and how we might need to stay on the problem for thirty-five years, and then you went and expected us to make the greatest discovery in the history of magic in the first hour we were working together. You didn't just hope, you really expected it. You're silly."

"Thank you. Now -"

"I've read all the books you gave me and I still don't know what to call that. Overconfidence? Planning fallacy? Super duper Lake Wobegon effect? They'll have to name it after you. Harry Bias."

"All right!"

"But it is cute. It's such a boy thing to do."

"Drop dead."

"Aw, you say the most romantic things."

Thud. Thud. Thud.

"So what's next?" said Hermione.

Harry rested his head against the bricks. His forehead was starting to hurt where he'd been banging it. "Nothing. I have to go back and design different experiments."

Over the last month, Harry had carefully worked out, in advance, a course of experimentation for them that would have lasted until December.

It would have been a great set of experiments if the very first test had not falsified the basic premise.

Harry could not believe he had been this dumb.

"Let me correct myself," said Harry. "I need to design one new experiment. I'll let you know when we've got it, and we'll do it, and then I'll design the next one. How does that sound?"

"It sounds like someone wasted a whole lot of effort."

Thud. Ow. He'd done that a bit harder than he'd planned.

"So," said Hermione. She was leaning back in her chair and the smug look was back on her face. "What did we discover today?"

"I discovered," said Harry through gritted teeth, "that when it comes to doing truly basic research on a genuinely confusing problem where you have no clue what's going on, my books on scientific methodology aren't worth crap -"

"Language, Mr. Potter! Some of us are innocent young girls!"

"Fine. But if my books were worth a carp, that's a kind of fish not anything bad, they would have given me the following important piece of advice: When there's a confusing problem and you're just starting out and you have a falsifiable hypothesis, go test it. Find some simple, easy way of doing a basic check and do it right away. Don't worry about designing an elaborate course of experiments that would make a grant proposal look impressive to a funding agency. Just check as fast as possible whether your ideas are false before you start investing huge amounts of effort in them. How does that sound for a moral?"

"Mmm... okay," said Hermione. "But I was also hoping for something like 'Hermione's books aren't worthless. They're written by wise old wizards who know way more about magic than I do. I should pay attention to what Hermione's books say.' Can we have that moral too?"

Harry's jaw seemed to be clenched too tightly to let any words out, so he just nodded.

"Great!" Hermione said. "I liked this experiment. We learned a lot from it and it only took me an hour or so."

"AAAAAAAAAAAAAAHHHHHHHHHHHHHHH!"

In the dungeons of Slytherin.

An unused classroom lit with eerie green light, much brighter this time and coming from a small crystal globe with a temporary enchantment, but eerie green light nonetheless, casting strange shadows from the dusty desks.

Two boy-sized figures in cowled grey cloaks (no masks) had entered in silence, and sat down in two chairs opposite the same desk.

It was the second meeting of the Bayesian Conspiracy.

Draco Malfoy hadn't been sure if he should look forward to it or not.

Harry Potter, judging by the expression on his face, didn't seem to have any doubts on the appropriate mood.

Harry Potter looked like he was ready to kill someone.

"Hermione Granger," said Harry Potter, just as Draco was opening his mouth. "Don't ask."

He couldn't have gone on another date, could he? thought Draco, but that didn't make any sense.

"Harry," said Draco, "I'm sorry but I have to ask this anyway, did you really order the mudblood girl an expensive mokeskin pouch for her birthday?"

"Yes, I did. You've already worked out why, of course."