It's funny how the cargo cult hides groupthink. Particularly the psychology of impostor syndrome. It's not just insecurity, it's got an underlying cause. The person affected realizes a truth: that there's a body of knowledge they lack, or they aren't accomplishing much but are still getting approval from their boss. Thats not some kind of "false impostor feeling", that's literally becoming aware of a truth about oneself, followed by fear of consequence.

When peers say "that's just impostor syndrome, don't worry about it!" they're reinforcing a groupthink that we should ignore the truth. The truth is that we often do excel despite our own shortcomings - but those shortcomings are real. We shouldn't hand-wave them away just to feel better, we should be focusing on improving ourselves.