Generalizing From One Example by Scott Alexander

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this is: Generalizing From One Example, published by Scott Alexander on the effective altruism forum.
Related to: The Psychological Unity of Humankind, Instrumental vs. Epistemic: A Bardic Perspective
"Everyone generalizes from one example. At least, I do."
-- Vlad Taltos (Issola, Steven Brust)
My old professor, David Berman, liked to talk about what he called the "typical mind fallacy", which he illustrated through the following example:
There was a debate, in the late 1800s, about whether "imagination" was simply a turn of phrase or a real phenomenon. That is, can people actually create images in their minds which they see vividly, or do they simply say "I saw it in my mind" as a metaphor for considering what it looked like?
Upon hearing this, my response was "How the stars was this actually a real debate? Of course we have mental imagery. Anyone who doesn't think we have mental imagery is either such a fanatical Behaviorist that she doubts the evidence of her own senses, or simply insane." Unfortunately, the professor was able to parade a long list of famous people who denied mental imagery, including some leading scientists of the era. And this was all before Behaviorism even existed.
The debate was resolved by Francis Galton, a fascinating man who among other achievements invented eugenics, the "wisdom of crowds", and standard deviation. Galton gave people some very detailed surveys, and found that some people did have mental imagery and others didn't. The ones who did had simply assumed everyone did, and the ones who didn't had simply assumed everyone didn't, to the point of coming up with absurd justifications for why they were lying or misunderstanding the question. There was a wide spectrum of imaging ability, from about five percent of people with perfect eidetic imagery1 to three percent of people completely unable to form mental images2.
Dr. Berman dubbed this the Typical Mind Fallacy: the human tendency to believe that one's own mental structure can be generalized to apply to everyone else's.
He kind of took this idea and ran with it. He interpreted certain passages in George Berkeley's biography to mean that Berkeley was an eidetic imager, and that this was why the idea of the universe as sense-perception held such interest to him. He also suggested that experience of consciousness and qualia were as variable as imaging, and that philosophers who deny their existence (Ryle? Dennett? Behaviorists?) were simply people whose mind lacked the ability to easily experience qualia. In general, he believed philosophy of mind was littered with examples of philosophers taking their own mental experiences and building theories on them, and other philosophers with different mental experiences critiquing them and wondering why they disagreed.
The formal typical mind fallacy is about serious matters of mental structure. But I've also run into something similar with something more like the psyche than the mind: a tendency to generalize from our personalities and behaviors.
For example, I'm about as introverted a person as you're ever likely to meet - anyone more introverted than I am doesn't communicate with anyone. All through elementary and middle school, I suspected that the other children were out to get me. They kept on grabbing me when I was busy with something and trying to drag me off to do some rough activity with them and their friends. When I protested, they counter-protested and told me I really needed to stop whatever I was doing and come join them. I figured they were bullies who were trying to annoy me, and found ways to hide from them and scare them off.
Eventually I realized that it was a double misunderstanding. They figured I must be like them, and the only thing keeping me from playing their fun games was that I was too shy. I figured they must be like me, a...