I am surprised that there is nothing about Impostor Syndrome on Robin Hanson's website, when to me it seems obviously connected to status. To use the standard formula: Impostor Syndrome is not about lack of skills.
(Also related to: humility, status regulation, unpopularity of nerds.)
Let me quote my older article:
Robin Hanson calls the two basic forms of status "dominance" and "prestige"; the fear-based and the admiration-based sources of social power respectively. He also notes how people high in "dominance" prefer to be perceived as (also) high in "prestige" [1, 2]. Simply said, a brutal dictator often wants to be praised as kind and smart and skilled (e.g. the "coryphaeus of science" Stalin), not merely powerful and dangerous.
[...] If you are not ready to challenge the chieftain for the leadership of the tribe, and if you don't want to risk being perceived as such, the safe behavior is to also downplay your skills as a hunter.
Although humans have two mechanisms of constructing social hierarchies, at the end of the day both of them compete for the same resource: power over people. Thus we see powerful people leveraging their power to also get acknowledged as artists or scientists; and successful artists or scientists leveraging their popularity to express political opinions.
The hierarchy of "dominance" is based on strength, but is not strength alone. The strongest chimp in the tribe can be defeated if the second-strongest and third-strongest join against him. Civilization makes it even more complicated. Stalin wasn't the physically strongest man in the entire Soviet Union.
(In theory, the most powerful person shouldn't need physical strength at all, if they have an army and secret police at command. But in practice, I suppose our instincts demand it; a physically weak leader would probably be a permanent magnet for rebellions. Therefore leaders flaunt their health and strength.)
Similarly, the hierarchy of "prestige" is based on skill, but is not skill alone. The most skilled person can be... what? Outskilled by a coalition of opponents? Nah, sounds like too much work. It is easier to stop them flaunting their skill, either by taking away their tools, or by threatening to break their arms and legs if you see them performing publicly again.
Which makes the prestige ladder a mixed one. To get on the top, you need a combination of superior skill and at least average dominance. If you are 10 at skill and 2 at dominance, you will probably be bullied into submission by someone who is 9 at skill and 7 at dominance. (Remember that dominance is not only physical strength; it also includes social power. Sticks and stones may break your bones, but Twitter can ruin your life.) No one applauds a talent who was too afraid to get on the stage.
What are you supposed to do then, if you happen to be 10 at skill and 2 at dominance, and your neighbor is 9 at skill and 7 at dominance and looks pissed off when you are around? Well, if you value your life, but can't increase your dominance, the solution is to downplay your skill and pretend to be at most 8; maybe even less just to be safe.
How is this all related to the Impostor Syndrome?
I suspect that Impostor Syndrome is simply an instinctive reaction to noticing that your skills are disproportionally high compared to your relative dominance at the workplace. This needs to stop, now! The most reliable way to convince others of your incompetence is to convince yourself. So you notice some imperfection of yourself or your work, and you exaggerate it in your mind until you feel like a complete idiot. Except you still have the prestigious job title, so now you fear you might be punished for that.
What predictions does this model make?
People with Impostor Syndrome are on average physically weaker or less popular or coming from less privileged backgrounds than people who feel like true masters (controlling for the actual level of skill).
Therapy based on "look, according to evidence X, you are really skilled" and "hey, nobody is perfect" will not work, unless it accidentally stumbles on something that makes the patient feel stronger or more popular. On the other hand, weightlifting will reduce the Impostor Syndrome, despite having no relation to the disputed skill.