I'm sure there are a few people lacking imposter syndrome who don't fall into that warning category, but in my experience, they're the exception. Imposter syndrome is pretty widespread among creative disciplines, including programming, writing, music, and art, partially because it is fueled by an errant perception (gestalt) of one's own abilities versus everyone else's. I think it is pretty safe to say, the overwhelming majority of programmers struggle with imposter syndrome; a number have just learned how to control it, but it never really totally goes away, since the gestalt is based on perception, not facts.
Case in point, I am very aware of how much I know, what I'm capable of, what I don't know, what I need to learn, and what I need to improve. But I still have to regularly counter my own imposter syndrome with the truth to keep it in check. I've yet to meet a successful (and non-egotistical) programmer, author, or artist who doesn't have the same struggle.
"Imposter Syndrome" is a common and widespread glitch in human psychology. Often (although not always), the ones who lack that glitch have a different gestalt: they swap the labels on the first diagram by David Whittaker in the post. Their perception is honestly that they know far more than everyone else, and act accordingly. They don't have imposter syndrome because they believe almost everyone except them is an imposter!
So, yes, there is the rare breed of programmer who is so grounded in reality, they have a realistic view of their own abilities and knowledge and a realistic view of others' abilities and knowledge. They just don't come along very often! Caution is still advisable, as little can do more harm to someone with imposter syndrome than to meet with an egotist.
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