But it's more nuanced than that.
I'm a Principal Engineer at a FAAMNG company. I have impostor syndrome all the time. Why? Because I measure myself against 1) role models that are ahead of me in many ways - I've always done that, and it's how I grow, 2) against those with strengths in areas that I have weaknesses.
I think my impostor syndrome is absolutely fact-based. I am not as good in the technical areas I care about as those I measure myself against.
My fallacy is that there is a billion things that I am good at, but I don't consider them difficult (how could they be, if I am good at them), or I consider them insufficient to a fully rounded engineer, if I don't also have the skills that I know I'm missing (but some of my peers are not).
It doesn't help that I'm the epitome of a 'Generalist' - I'm good at a lot of things, but I don't know if I'm the BEST at anything.
I get lots of positive reinforcement - from my management chain, and from those more junior than me. But it never resonates. I always think "damn, I've actually fooled them all". And then I feel guilty that the management is putting so much trust in me, and that the juniors actually look up to a fraud.
The only feedback that resonates is from my technical peers. Luckily I get this just often enough that I don't fall into a catatonic mess of anxiety. And sometimes I believe it...