Harry Potter and the Methods of Rationality

(some might even say cute) ensconced behind a vegetable stall that was behind a magical glove shop that was on an alleyway off a side street of Diagon Alley. Disappointingly, the shopkeeper was not a wizened ancient crone; just a nervous-looking young woman wearing faded yellow robes. Right now she was holding out a Moke Super Pouch QX31, whose selling point was that it had a Widening Lip as well as an Undetectable Extension Charm: you could actually fit big things in it, though the total volume was still limited.

Harry had insisted on coming here straight away, first thing - insisted as hard as he thought he could without making Professor McGonagall suspicious. Harry had something he needed to put into the pouch as soon as possible. It wasn't the bag of Galleons that Professor McGonagall had allowed him to withdraw from Gringotts. It was all the other Galleons that Harry had surreptitiously shoved into his pocket after falling into a heap of gold coins. That had been a real accident, but Harry was never one to discard an opportunity... though it'd really been more of a spur-of-the-moment thing. Ever since Harry had been awkwardly carrying the allowed bag of Galleons next to his trouser pocket, so that any jingling would seem to come from the right place.

This still left the question of how he was actually going to get the other coins into the pouch without getting caught. The golden coins might have been his, but they were still stolen - self-stolen? Auto-thieved?

Harry looked up from the Moke Super Pouch QX31 on the counter in front of him. "Can I try this for a bit? To make sure it works, um, reliably?" He widened his eyes in an expression of boyish, playful innocence.

Sure enough, after ten repetitions of putting the coin-bag into the pouch, reaching in, whispering "bag of gold", and taking it out, Professor McGonagall took a step away and began examining some of the other items in the shop, and the shopkeeper turned her head to watch.

Harry dropped the bag of gold into the mokeskin pouch with his left hand; his right hand came out of his pocket tightly holding some of the gold coins, reached into the mokeskin pouch, dropped the loose Galleons, and (with a whisper of "bag of gold") retrieved the original bag. Then the bag went back into his left hand, to be dropped in again, and Harry's right hand went back into his pocket...

Professor McGonagall looked back at him once, but Harry managed to avoid freezing or flinching, and she didn't seem to notice anything. Though you never did quite know, with the adults that had a sense of humour. It took three iterations to get the job done, and Harry guessed he'd managed to steal maybe thirty Galleons from himself.

Harry reached up, wiped a bit of sweat from his forehead, and exhaled. "I'd like this one, please."

Fifteen Galleons lighter (twice the price of a wizard's wand, apparently) and one Moke Super Pouch QX31 heavier, Harry and Professor McGonagall pushed their way out of the door. The door formed a hand and waved goodbye to them as they left, extruding its arm in a way that made Harry feel a bit queasy.

And then, unfortunately...

"Are you really Harry Potter?" whispered the old man, one huge tear sliding down his cheek. "You wouldn't lie about that, would you? Only I'd heard rumours that you didn't really survive the Killing Curse and that's why no one ever heard from you again."

...it seemed that Professor McGonagall's disguise spell was less than perfectly effective against more experienced magical practitioners.

Professor McGonagall had laid a hand on Harry's shoulder and yanked him into the nearest alleyway the moment she'd heard "Harry Potter?" The old man had followed, but at least it looked like no one else had heard.

Harry considered the question. Was he really Harry Potter? "I only know what other people have told me," Harry said. "It's not like I remember being born." His hand brushed his forehead. "I've had this scar as long as I remember, and I've been told my name was Harry Potter as long as I remember. But," Harry said thoughtfully, "if there's already sufficient cause to postulate a conspiracy, there's no reason why they wouldn't just find another orphan and raise him to believe that he was Harry Potter -"

Professor McGonagall drew her hand over her face in exasperation. "You look just about exactly like your father, James, the year he first attended Hogwarts. And I can attest on the basis of personality alone that you are related to the Scourge of Gryffindor."

"She could be in on it too," Harry observed.

"No," quavered the old man. "She's right. You have your mother's eyes."

"Hmm," Harry frowned. "I suppose you could be in on it too -"

"Enough, Mr. Potter."

The old man raised up a hand as if to touch Harry, but then let it fall. "I'm just glad that you're alive," he murmured. "Thank you, Harry Potter. Thank you for what you did... I'll leave you alone now."

And his cane slowly tapped away, out the alley and down the main street of Diagon Alley.

The Professor looked around, her expression tense and grim. Harry automatically looked around himself. But the alley seemed empty of all but old leaves, and from the mouth leading out into Diagon Alley, only swiftly striding passersby could be seen.

Finally Professor McGonagall seemed to relax. "That was not well done," she said in a low voice. "I know you're not used to this, Mr. Potter, but people do care about you. Please be kind to them."

Harry looked down at his shoes. "They shouldn't," he said with a tinge of bitterness. "Care about me, I mean."

"You saved them from You-Know-Who," said Professor McGonagall. "How should they not care?"

Harry looked up at the witch-lady's strict expression beneath her pointed hat, and sighed. "I suppose there's no chance that if I said fundamental attribution error you'd have any idea what that meant."

"No," said the Professor in her precise Scottish accent, "but please explain, Mr. Potter, if you would be so kind."

"Well..." Harry said, trying to figure out how to describe that particular bit of Muggle science. "Suppose you