Yeah, but there's also correlations. If someone is "stupid" in one area, they are much more likely to be "stupid" in another area as well. It's not a guarantee, but it's highly probable.
Success in one area typically correlates with success in many other areas as well. Otherwise we wouldn't have polymaths. There are people who are among the best in the world in fields that are completely independent.
This is not true in my experience. It's just as likely that someone's "intelligence" in one area gives them a false sense of their ability to understand other areas. They'll jump into some unrelated or semi-related area, learn a little, and quickly act as if they understand it as well as the understand their main area of expertise.
This is especially true if the new area is something they're peripherally familiar through everyday experience. I'm a teacher, so teaching comes to mind, here. Everyone has opinions about teaching and learning because everyone spent 15-20 years of their life doing it.
Intelligent people often act as if
Understanding of Area A + Familiarity with Area B = Understanding of Area B
But as Hegel said, "The familiar is not understood precisely because it's familiar."
See also: every thread ever on HN about law, politics, race, or gender.
In my experience, one's ability to develop expertise in many fields has much more to do with one's temperament. Most people I've met who who are able to do this live in a kind of visceral, mortal fear that they might believe something that isn't true. They're more likely to see certainty (in others as well as themselves) as a symptom of utter, hopeless confusion than as a symptom of understanding.
Success breeds success, yes. And some people are truly more talented than others, yes. But it still leaves tremendous gaps for the stupid to occur.
Consider the recent story about how Elon Musk (arguably the most brilliant polymath of our era) chewed out an employee for missing a work function attend the birth of his child. That's appallingly stupid. That's pure blindness to instinct, cultural values, and compassion. There you go. Elon Musk, fscking idiot.
More generally, a lot of people with brilliant technical skills have lousy social skills - social failings that can drag a team's effectiveness down as much as a technical idiot can.
And more than that, I'd say. People who are truly brilliant in one area can often get away with being absolutely, irredeemably stupid in another because nothing in their environment ever forces them to deal with their stupidity.
A brilliant engineer can have an amazing, world-changing technical career without ever realizing that he'd be 10x more effective with better social and leadership skills. Whether one sees that truth about themselves has much more to do with their personality and temperament than it does with their intelligence or expertise (IMO).
I'm not a Musk-apologist, but he already denied that vehemently on Twitter. And the "source" of that statement is anonymous with little credibility. Seems like an easy case of libel.
Polymaths exist, but are not the norm. I've more often run across the opposite, where people who are good in one area are not good at all in another. For example many people who are very good programmers are very poor salespeople, and vice-versa, which is one reason you don't have your sales team and your programming team be the same. Good programmers and good documentation writers are often not the same people either. At least among my colleagues, I definitely have a sense that I should ask A for some things, and B for others.
Success in one area typically correlates with success in many other areas as well. Otherwise we wouldn't have polymaths. There are people who are among the best in the world in fields that are completely independent.