If you've seen the movie Wolf of Wall Street I saw an interview with the real guy and he said he literally always feels like he has no idea what he's doing. I forget who he was talking to, but the other guy was also very successful and he said the same thing. The real smart people never know what's gonna happen next. You just have to rely on your ability to learn an act. If you don't feel this way you probably have a boring life with a low paying job. You aren't using your brain at all and already know all the answers. Feeling stupid is actually quite a good thing. You're only gonna feel that way when you are challenging yourself.