I used to have imposter syndrome when I first started at my current job. But then I discovered that one of my coworkers was an actual imposter. He didn't lie on his resume or anything but he was basically incapable of thinking for himself. If there was no step-by-step process to follow, he'd spin his wheels for weeks before doing it in the worst possible way, refusing all offers of assistance from the rest of our team.

After he quit and the true extent of his incompetence came to light, I no longer felt like an imposter.