It's not like this is the only serious blind spot he has regarding Quirrell, though, is it?
My current theory seems almost obvious, after I coincidentally decided to reread HPMOR myself shortly after rereading Chamber of Secrets with my daughter:
Early in Chamber of Secrets, a Death Eater gives Tom Riddle's horcrux, a nearly-indestructable magical diary, to Ginny. One of the powers that diary has is to take partial control of her as she reads it intently over the coming year, and one of the ways that control manifests itself is to make it difficult for her to even think about what's going on with the diary or the blind spots it's creating in her mind.
Early in HPMOR, a Death Eater (who is probably Tom Riddle) gives a nearly-indestructible magical diary to Harry. Harry clearly wants to read it intently, but we never see what happens when he tries, and later (because he'd need to learn Latin first? really??) he hardly even thinks about it, or about a couple other obvious blind spots in his mind, again.
I suspect that Quirrelmort was handing Harrymort a horcrux as yet another way to try to turn him to the dark side, and although that didn't work, even temporarily clouding Harry's better judgement about a few key topics is a decent secondary benefit.
It's not really a blind spot against Quirrell. If what Quirrell says it's true and Quirrell dies soon, it's important information to acquire from him.
There no time pressure to read the diary. There's time pressure to get information from Quirrell. It requires an environment where Quirrell can cast the spells against eavesdropping.
New chapter, and the end is now in sight!
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 103.
There is 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.)
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: