Maturity and competence are not the same thing.
Immaturity may not be precisely correct, but he's definitely not accusing her of incompetence. Irresponsibility, perhaps. He's not saying that she tried and failed, he's saying that she didn't try. He's saying that she's just blindly playing a role, instead of actually acting responsibly, and that it's so hard-wired into her that it's not even worth him trying to correct it. Hard-wired irresponsibility is close enough to immaturity that it's a reasonable approximation.
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 90. The previous thread has passed 750 comments.
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.)
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: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18,19.
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: