Yes and no, to the idea that people are individuals and can't be analyzed quantitatively in large numbers. Certainly statistical abstraction of humans is the foundation of advertising and marketing, and consequently because advertising controls it, entertainment. It pays off in real money for those industries, so there must be something to it. The alignment of advertising, business, and entertainment into a partnership ensures a high degree of uniformity in those significant areas of human life.

I think that there's a second hypothesis I can make: That the creation of a highly uniform mass culture affects people's behavior and thinking, and in turn produces more uniformity in the population. Even highly individualistic people can be worn down by the thousands of small aspects of life that tend toward uniformity and present obstacles to individualism. Greater uniformity in the population makes statistical abstraction more accurate, making manipulative techniques like advertising more effective, which in turn keeps up the pressure on the population toward uniformity and away from individuality.

We've discussed manipulation in advertising before, and I was surprised that you don't believe it exists or that it could possibly be effective. I'd warn you against hubris: If you don't see any manipulation at all in advertising, you may be most vulnerable to it. I know you pride yourself on your individuality, and I'm just saying that that pride may be a vulnerability. In this area, perhaps you're not paranoid enough? They really are out to get you--noting that advertisers are out to get your money is not at all paranoid.

To get back to the Big Idea, I think that attempts at "psychohistory" don't take place in a vacuum, that they interact with the population being analyzed--the observer effect--to gradually over time make the population easier to manage with "applied psychochistory". Psychohistory is doomed to succeed.

On the idea of exceptionalism, of unique individuals who change history, of course that's an observable fact. Though it may not fully take into account the necessity of being in the right place at the right time. History remembers the exceptional individuals who existed in an environment that gave them what they needed to achieve, but what about the very similar individuals born before their time or someplace where they had no opportunity to change history? Individuals may be unique, but they don't exist outside of the flows and forces that we're talking about. "Fortune favors the prepared mind", "there is a tide in the affairs of men"...lots of human folk wisdom addresses this very point.

Even then I'm not totally denying the possibility of uniqueness overcoming all. I can't help but characterize humans and our history as chaotic, and chaos theory allows for strange attractors and metastable states and all sorts of unique or psuedo-unique states.

Then there's the butterfly effect. The flip side of exceptionalism is "for want of a nail", that some tiny occurrence can be amplified through chains of causality to produce huge effects. The stable boy who failed to shoe the horse might have been utterly unexceptional, yet occupied an exceptional place in history.

In real life, there are "Mules" in our history every day.

That's the paradox that tripped up the Second Foundation: They forgot that exceptions arise "every day", making exceptions the rule, and something which should have been included in the equations.

Asimov wrote decades before chaos theory, so he wouldn't have seen metastable states and the sudden flipping between states, and the butterfly effect, as normal features of reality. He wrote in a real milieu that was still more conceptually Newtonian than quantum. I'll bet that if he'd written Foundation today, he'd have had to find some other plot device to create conflict in the second half of the epic. I'd have trouble buying a modern psychohistory that didn't account for chaotic behavior, and characters who were surprised to find themselves surprised.

So, yes and no: I'd say that Asimov's linear psychohistory was a fantasy, but a modern nonlinear psychohistory based on chaos and interacting with an ever-more-predictable population, will inevitably succeed.