Harry Potter and the Methods of Rationality

"Not many," said Harry. He'd only recently realized... "Not nearly enough."

"Then I will observe," said Professor Quirrell, "that you do not find out all there is to know about a man by asking only his friends."

Now it was Harry's turn to walk a few steps in silence on the slightly beaten dirt path that led back to Hogwarts. He'd really been supposed to know better than that already. Confirmation bias was the technical term; it meant, among other things, that when you chose your information sources, there was a notable tendency to choose information sources that agreed with your current opinions.

"Thank you," Harry said. "Actually... I didn't say it earlier, did I? Thank you for everything. If another Dementor ever threatens you, or for that matter, slightly annoys you, just let me know and I'll introduce it to Mister Glowy Person. I don't like it when Dementors slightly annoy my friends."

That got him an indecipherable glance from Professor Quirrell. "You destroyed the Dementor because it threatened me?"

"Erm," Harry said, "I'd sort of decided on it before then, but yes, that would have been sufficient reason by itself."

"I see," said Professor Quirrell. "And what would you have done about the threat to me if your spell hadn't worked for destroying the Dementor?"

"Plan B," said Harry. "Encase the Dementor in dense metal with a high melting point, probably tungsten, drop it into an active volcano, and hope it ends up inside Earth's mantle. Ah, the whole planet is filled with molten lava under its surface -"

"Yes," said Professor Quirrell. "I know." The Defense Professor was wearing a very odd smile. "I really should have thought of that myself, all things considered. Tell me, Mr. Potter, if you wanted to lose something where no one would ever find it again, where would you put it?"

Harry considered this question. "I suppose I shouldn't ask what you've found that needs losing -"

"Quite," said Professor Quirrell, as Harry had expected; and then, "Perhaps you will be told when you are older," which Harry hadn't.

"Well," said Harry, "besides trying to get it into the molten core of the planet, you could bury it in solid rock a kilometer underground in a randomly selected location - maybe teleport it in, if there's some way to do that blindly, or drill a hole and repair the hole afterward; the important thing would be not to leave any traces leading there, so it's just an anonymous cubic meter somewhere in the Earth's crust. You could drop it into the Mariana Trench, that's the deepest depth of ocean on the planet - or just pick some random other ocean trench, to make it less obvious. If you could make it buoyant and invisible, then you could throw it into the stratosphere. Or ideally you would launch it into space, with a cloak against detection, and a randomly fluctuating acceleration factor that would take it out of the Solar System. And afterward, of course, you'd Obliviate yourself, so even you didn't know exactly where it was."

The Defense Professor was laughing, and it sounded even odder than his smile.

"Professor Quirrell?" Harry said.

"All excellent suggestions," said Professor Quirrell. "But tell me, Mr. Potter, why those exact five?"

"Huh?" said Harry. "They just seemed like the obvious sorts of ideas."

"Oh?" said Professor Quirrell. "But there is an interesting pattern to them, you see. One might say it sounds like something of a riddle. I must admit, Mr. Potter, that although it has had its ups and downs, on the whole, this has been a surprisingly good day."

And they continued walking down the path that led to the gates of Hogwarts, quite some distance apart; as Harry, without even thinking about it, automatically stayed far enough away from the Defense Professor not to trigger that sense of doom, which for some reason seemed unusually strong right now.

Aftermath, Daphne Greengrass:

Hermione had refused to answer any questions, and as soon as they'd passed the split leading to the Slytherin dungeons, Daphne and Tracey had peeled off at once, walking as quickly as they could. Rumor traveled fast in Hogwarts, so they'd have to go to the dungeons right away if they wanted to be the first to tell everyone the story.

"Now remember," said Daphne, "don't just blurt out about the kiss as soon as we walk in, okay? It works better if we tell the whole story in order."

Tracey nodded excitedly.

And as soon as they burst into the Slytherin common room, Tracey Davis took a deep breath and shouted, "Everyone! Harry Potter couldn't cast the Patronus Charm and the Dementor almost ate him and Professor Quirrell saved him but then Potter was all evil until Granger brought him back with a kiss! It's true love for sure!"

It was ordered storytelling of a sort, Daphne supposed.

The news failed to produce the expected reaction. Most of the girls glanced over and then stayed in their couches, or the boys simply kept reading in their chairs.

"Yes," said Pansy sourly, from where she was sitting with Gregory's feet in her lap, leaning back and reading what seemed to be a coloring book, "Millicent already told us."

How -

"Why didn't you kiss him first, Tracey?" said Flora and Hestia Carrow from their own chairs. "Now Potter's going to marry a mudblood girl! You could've been his true love and gotten into a rich Noble House and everything if you'd just kissed him first!"

Tracey's face was a picture in stunned realization.

"What?" shrieked Daphne. "Love does not work like that!"

"Of course it does," stated Millicent from where she was practicing some sort of Charm while looking out a