"I'm trying to think if there's anything I should be doing right now," said Harry Potter. "It's hard, though. My mind keeps on imagining ways the past could have gone differently if I'd thought faster, and I can't rule out that there might be a key insight in there somewhere."

I'd misremembered this-- I thought he'd been trying to get his mind off his possible mistakes, but couldn't, and I get the impression that the people in this part of the discussion didn't think he'd even been trying to get his mind off possible mistakes.

Actually, he wasn't sure where the answer lies, so thinking about his past mistakes might actually offer a useful clue, though I wonder whether his mind is drawn to the topic more than it should be.

It's also possible that this discussion is using HPMOR as springboard to talk about the problem of attending too much to past mistakes rather than trying to find solutions.