If imposter syndrome doesn’t go away with time, it is very possible the person overly focuses on knowledge/skills that are lacking but that are not required at all to perform at their job, and this can happen even when the person already is a/the top performer.
I've spent a large part of my career managing IT teams. I've worked with a lot of noobs. The issue I find more often is not that they don't know the info, they simply don't have the confidence in what they know and no real practice applying it.
It's one thing to know that DNS travels over port 53, but leveraging that in troubleshooting is harder, since it may involve a firewall, switches, trunked ports, servers, workstations, etc.
It just takes time to learn the practical side and that's rarely taught in schools from what I've seen.
