I've taken quite a few psychology courses in pursuit of my undergrad as electives, as I felt it fit quite well with business and marketing, and this is the first time I've heard about this (or it just dropped from my memory bank). So naturally, I had to Google it.
Definition:
Imposter syndrome is a psychological phenomenon characterized by persistent feelings of self-doubt, inadequacy, and fear of being exposed as a fraud, despite objective evidence of one's abilities and achievements.
Having read that and have work experience in a lot of fields, I've become a master at a lot of trades. That said, I would take a hybrid approach as to what
@Shawn said along with reminding myself that I can instruct because I know what I am doing, but I also understand I am never fully an expert at anything and never will be, as there's always new information to learn and grow from.
There are times when subordinates come along and question me, and I've learned even more from them, as I take their past knowledge and expertise into decision-making consideration too, as any great leader should. The feeling of being questioned, even as an expert, should be looked at positively as a method of self-growth, if in the end, they are right.
Having said that, there is a fine line between a subordinate having malicious intent to try and knock you down a peg, but more often than not, that's not the case as you all have an overall shared goal or objective to achieve together. If your leaders are also great, they will recognize the narcissistic trait of the subordinate if they try to go around you, believing that they will be praised or promoted; instead, those leaders will often take a mental note that the subordinate doesn't respect authority, and it will likely harm them more than help them if you didn't address the concerns that they had, and brought directly to your attention first, which could have achieved the objective more efficiently.