Lesson learned from HPMOR, only months after… (spoilers from beginning to end)

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.