When I was preparing for Defcon, one thing I read was imposter syndrome was a common feeling for newbies. There are so many people there that are so skilled, and it makes people feel like they don't belong.
I didn't feel like an imposter while I was there. At least, not in the way it's normally expressed. Skills or knowledge is not what I felt inadequate about.
I felt like I didn't belong because I didn't feel like I had the energy and drive to keep pace.