I'm not entirely convinced. If Quirrell has a weakness (note, I did say "if"), then it's his lack of empathy with children, and especially Muggle-born children. Harry is able to consistently surprise him (f.ex. in Azkaban, or by cheering him up at the end of the bully saga, etc.), and I didn't get the impression that this is because Harry is some sort of an uber-outlier. He's an outlier, yes, but he's still a human kid.
This weakness probably stems from Quirrell's cynicism, which a few characters have already commented upon. Qurrell subconsciously assumes that everyone is acting like a perfectly rational agent that attempts to maximize its own expected utility by enhancing its power to manipulate external reality (which occasionally includes other actors). In Quirrell's subset of the world, this assumption is quite often correct, but most real people -- such as Hermione -- do not, in fact, act that way all of (or even most of) the time.
Qurrell subconsciously assumes that everyone is acting like a perfectly rational agent that attempts to maximize its own expected utility by enhancing its power to manipulate external reality
He definitely doesn't think so consciously; one of his more memorable quotes is something along the lines of "The main thing ordinary people do, Mr. Potter, is nothing".
Update: Discussion has moved on to a new thread.
The hiatus is over with today's publication of chapter 73, and the previous thread is approaching the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it.
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. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
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: