I got my Ph.D. not too long ago. I was looking for a job in industry during the Summer, but didn't find anything that interested me with a compatible set of "mimimum requirements". Lately, I've been looking for postdocs, but even there, when I read the job requirements, I don't think that I measure up. I feel like I cheated my way through my Ph.D.. I'm pretty sure that's not true, but the feeling becomes stronger every day. I feel like I have no idea how to do anything useful, and that I don't understand even the basics, so why should even a university hire me as a postdoc. How common is this feeling?