Harry Potter and the Methods of Rationality

Harry was examining the wizarding equivalent of a first-aid kit, the Emergency Healing Pack Plus. There were two self-tightening tourniquets. A Stabilisation Potion, which would slow blood loss and prevent shock. A syringe of what looked like liquid fire, which was supposed to drastically slow circulation in a treated area while maintaining oxygenation of the blood for up to three minutes, if you needed to prevent a poison from spreading through the body. White cloth that could be wrapped over a part of the body to temporarily numb pain. Plus any number of other items that Harry totally failed to comprehend, like the "Dementor Exposure Treatment", which looked and smelled like ordinary chocolate. Or the "Bafflesnaffle Counter", which looked like a small quivering egg and carried a placard showing how to jam it up someone's nostril.

"A definite buy at five Galleons, wouldn't you agree?" Harry said to Professor McGonagall, and the teenage salesgirl hovering nearby nodded eagerly.

Harry had expected the Professor to make some sort of approving remark about his prudence and preparedness.

What he was getting instead could only be described as the Evil Eye.

"And just why," Professor McGonagall said with heavy scepticism, "do you expect to need a healer's kit, young man?" (After the unfortunate incident at the Potions shop, Professor McGonagall was trying to avoid saying "Mr. Potter" while anyone else was nearby.)

Harry's mouth opened and closed. "I don't expect to need it! It's just in case!"

"Just in case of what?"

Harry's eyes widened. "You think I'm planning to do something dangerous and that's why I want a medical kit?"

A look of grim suspicion and ironic disbelief was the answer.

"Great Scott!" said Harry. (This was an expression he'd learned from the mad scientist Doc Brown in Back to the Future.) "Were you also thinking that when I bought the Feather-Falling Potion, the Gillyweed, and the bottle of Food and Water Pills?"

"Yes."

Harry shook his head in amazement. "Just what sort of plan do you think I have going, here?"

"I don't know," Professor McGonagall said darkly, "but it ends either in you delivering a ton of silver to Gringotts, or in world domination."

"World domination is such an ugly phrase. I prefer to call it world optimisation."

This hilarious joke failed to reassure the witch giving him the Look of Doom.

"Wow," Harry said, as he realised that she was serious. "You really think that. You really think I'm planning to do something dangerous."

"Yes."

"Like that's the only reason anyone would ever buy a first-aid kit? Don't take this the wrong way, Professor McGonagall, but what sort of crazy children are you used to dealing with?"

"Gryffindors," spat Professor McGonagall, the word carrying a freight of bitterness and despair that fell like an eternal curse on all youthful enthusiasm and high spirits.

"Deputy Headmistress Professor Minerva McGonagall," Harry said, putting his hands sternly on his hips. "I am not going to be in Gryffindor -"

At this point the Deputy Headmistress interjected something about how if he was she would figure out how to kill a hat, which odd remark Harry let pass without comment, though the salesgirl seemed to be having a sudden coughing fit.

"- I am going to be in Ravenclaw. And if you really think that I'm planning to do something dangerous, then, honestly, you don't understand me at all. I don't like danger, it is scary. I am being prudent. I am being cautious. I am preparing for unforeseen contingencies. Like my parents used to sing to me: Be prepared! That's the Boy Scout's marching song! Be prepared! As through life you march along! Don't be nervous, don't be flustered, don't be scared - be prepared!"

(Harry's parents had in fact only ever sung him those particular lines of that Tom Lehrer song, and Harry was blissfully unaware of the rest.)

Professor McGonagall's stance had slightly softened - though mostly when Harry had said that he was heading for Ravenclaw. "What sort of contingency do you imagine this kit might prepare you for, young man?"

"One of my classmates gets bitten by a horrible monster, and as I scrabble frantically in my mokeskin pouch for something that could help her, she looks at me sadly and with her last breath says, 'Why weren't you prepared?' And then she dies, and I know as her eyes close that she won't ever forgive me -"

Harry heard the salesgirl gasp, and he looked up to see her staring at him with her lips pressed tight. Then the young woman whirled and fled into the deeper recesses of the shop.

What...?