Contact between Harry and Quirrell causes mutual destruction.
I had wondered if Harry was a time turned version of Quirrell, and the "sense of doom" was a feeling about interaction with a time turned version of yourself.
All the information I needed was there all along
Along those lines, my biggest failing was taking Quirrellmort as so invincible. Get the drop on him and stun him. Thoroughly erase his memories. Duh. The whole "can't be killed" and "can escape his body" were effective brains stops for me.
A good lesson on being clear about your requirements. He didn't need to be killed, he needed to be removed as a threat.
Interesting. For the BSG fans, funny how the Cylons had their own horcrux network.
Surely that the older Quirrell had time turned and met his younger self?
Added: oh, I see, it works both ways.
I, for one, hoped he was simply Quirrell, the genius. And somewhere out there was Voldemort, the evil genius, doing things to all those people in Asia who were mentioned once or twice.
This seems to be the sort of cue that is much more reliable in fiction than in real life. In real life, not everything that happens has to be foreshadowed.
And conversely, things are allowed to just happen Because the Author Says So in fiction. When watching TV, I'll often ask "why didn't person X just do obvious thing Y which would have solved all of their problems for the rest of this episode?", to which my girlfriend's perfectly valid response is "plot reasons" (TV Tropes calls this the Anthropic Principle)
I think I agree with your core point. However:
You can't always ask why. I would have liked to see you talk about this and why you think there was enough evidence to ask why in the example you give.
In retrospect, I believe it was obvious
I don't think obvious is the right word. A lot of smart readers missed out on it too. To me, the more interesting question is why it seems obvious.
Again, I think I agree with your core point and I'm nitpicking a little, but I think the points are worth making.
I can't deny that hindsight bias may be working, despite my awareness of it.
What I can say for sure is that I did in fact never even seek a causal, reductionist explanation for the mysterious dark side or the Q-H resonance, in a cognitive error I see as very comparable to the Wizengamot just accepting that Dementor-scaring was a "Boy-Who-Lived quality" without any explanation.
While it now seems to me that I could have deduced it, that part may be totally false. I didn't even suspect Quirrell until I read about other people doing so. :/
The lesson I have just recently gleaned from the 81st chapter of HPMOR along with Harry's observations of the sense of doom he feels around Voldemort.
Chapter 81: "For whatever reason, then, most of the Wizengamot has never walked the path that leads to powerful wizardry; they do not seek out what is hidden. For them, there is no why. There is no explanation. There is no causality. The Boy-Who-Lived, who was already halfway into the magisterium of legend, has now been promoted all the way there; and it is a brute fact, simple and unexplained, that the Boy-Who-Lived frightens Dementors. Ten years earlier they were told that a one-year-old boy defeated the most terrible Dark Lord of their generation, perhaps the most evil Dark Lord ever to live; and they just accepted that too."
All the information I needed was there all along, but only now do I perceive the pattern this information indicates.
In retrospect, I believe it was obvious that Quirrell was Voldemort. But, at least in my own mind, the oft-repeated note of the sense of doom was filed under the same list of acausal phenomena as was Harry's Dementor-scaring by the Wizengamot.
What I ought to have done, what I was fully capable of doing (if hindsight bias is not plaguing me (not too much, anyway)), was thinking:
"Ah, a sense of doom which is felt mutually and only by Harry and Quirrell. Why should that be?"
And then, still more in the Stanford Prison Experiment Arc
"Ah, I see, it all falls into place. Contact between Harry and Quirrell causes mutual destruction. Why should that be (the phrase which was missing from my mind in every instance of the manifestation of the sense of doom)? They must be connected somehow. Why, yes, actually we already know that they are. As Harry pointed out, he and Quirrell have similar minds; Quirrell is his superior in his very own way of thinking, very much as if Quirrell was a grown-up version of Harry. No, that doesn't sound quite right, I don't see Harry growing up that way. Just a grown-up version of his dark side, I suppose. Why does Harry have a dark side, anyway? (This was another phenomenon I classified as acausal, filed along with the Just So Stories). Nobody else does, what's different about Harry? He's had it his whole life, could he have been born with it? No, no apparent reason for his parents to have such a child, perhaps just early in life. Just early in his life, I suppose. Now what could it be...
And here, I hope it is clear that I am belaboring the point, that I probably could have leapt to the conclusion with far fewer steps of consideration in between.
And so, having read of the cognitive error, and comprehended it, I did not realize that I had been committing it so recently; not until months after all the necessary information was already inputted did my processing manage to output the answer.