Certainly, the planning fallacy applies. And even if, for example, arbitrage worked the way it seems, and without the extra pitfalls that have been mentioned, there's a lot more to it than just swapping silver for gold and back. Harry's 11, he can't leave Hogwarts, his finances are tightly controlled by Dumbledore, 100,000 galleons = 1.7 million sickles ~= 17 tonnes of silver. Your dad doesn't just slip that into his back pocket. You're going to need help lifting it, security to guard it, vehicles to move it...
On the other hand, Harry has a lot of resources that haven't even been mentioned yet. There's a house in Godricks hollow for example, and the Granger's would probably be willing to contribute.
He hasn't even really made an accurate count of his vault. He described the stacks as a rough pyramid, but then estimates they're 20 wide and 60 tall - so in other words, each step of the pyramid is only three coins high. I made a small model out of poker chips, and it looks more like a flat than a stack. If it were a normal author, I'd figure the description was bad and the "estimate" was spot on, but EY is smart enough to realize that estimates aren't that accurate. Harry might have underestimated and already have 100,000. Of course, he might have over estimated instead.
Maybe he should learn a magical counting spell.
and the Granger's would probably be willing to contribute.
A good chance they could pay off the entire debt. They seemed very well off.
I've got a friend who is a dentist. He could pay it off if he wanted to. 2 dentists? If they had decent business sense, it wouldn't be a problem. This is in the US, however. I'd guess that pay scales are different in Britain.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 81, which should be published later today. The previous thread passed 400 comments as of the time of this writing, so it will pass 500 comments soon after the next chapter is posted, if not before. I suggest refraining from commenting here until chapter 81 is posted; comment in the 12th thread until you read chapter 81. After chapter 81 is posted, I suggest all discussion of previous guesses be kept here, with links to comments in the previous thread.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.) When posted, chapter 81 should appear here.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven, eight,nine, ten, eleven, twelve.
As a reminder, it’s often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: