Minerva McGonagall and Harry go shopping for his school things in Diagon Alley. He discovers more information about Voldemort from her, all while purposefully buying things he might need in case of emergency.

Title meaningEdit

The Planning Fallacy refers to the human tendency to be overly optimistic when it comes to things like planning how long tasks will take, what kinds of terrible things happen to people, and so on. In this case, it refers to Professor McGonnagall's perception that Harry is being overly pessimistic or fearful as evidenced by his purchasing medical and first-aid supplies, when in fact one has to be very pessimistic to have one's predictions be worse than reality.

Title quoteEdit

You think your day was surreal? Try mine.

Detailed chapter synopsisEdit

Harry is in Diagon Alley with Professor McGonagall, trying to figure out how the mokeskin pouch works. She is befuddled by his line of scientific inquiry. He discovers how rare Muggleborn witches and wizards are, and plots to take over the Magical world.

After purchasing most of his school supplies, Harry wants to buy an Emergency Healing Pack Plus. McGonagall asks why he would need this, and he explains the Planning Fallacy. He also realizes that she thought he was buying things because he was plotting something dangerous, and he explains that is not the case at all.

McGonagall suspects something traumatic has happened to him because he is so strange, perhaps abuse. He gets very angry at this wrongful accusation and demands she retract her insinuations. He explains why he has always felt alone, because his intelligence is not matched by other children, and not seen or respected by adults.

Harry retrieves his wand, complete with Phoenix feather, and starts discussing Voldemort playfully, but unfortunately infers from McGonagall's reaction that Voldemort is still alive and that there is a prophecy about he and Harry. He blacmails McGonagall into giving out more information, but gives her time to think.

He then has a great opportunity to prove his point about adults not respecting his intelligence when the trunk he wants costs a little more than he was allowed to take from his vault. He reveals that he had pocketed more than she would have allowed, and buys the trunk. McGonagall earns his respect by seeing his reasoning.

The chapter ends with Harry leaving The Leaky Cauldron as McGonagall suggests that he look for Hermione Granger on the train.


In this chapter, we learn that Voldemort is still alive, and that there is a prophecy regarding him and Harry.

Harry thinks that the best way to escape from Azkaban would be not to go there. There is a fan theory that indeed, Sirius Black never went to Azkaban; if so, this is the first hint.


Harry Potter-Evans-Verres

Minerva McGonagall


Della (Salesgirl)

Unnamed Salesman

Albus Dumbledore

Sirius Black (mentioned only)

Voldemort (mentioned only)

Hermione Granger (mentioned only)


Diagon Alley

The Leaky Cauldron


Mokeskin pouch

Rationality and scienceEdit

The Planning Fallacy

Artificial Intelligence

Author notesEdit

External linksEdit