Wow, great question. And such a coincidence that I just posted an article about my single best piece of advice. I would say very simply, that you're not an impostor in the world of software development. You're a problem solver, and that combined with the fact that you enjoy doing it is what defines your value as a software engineer. The rest is just gaining knowledge, and passing through the fear of stretching that knowledge in search of solutions to problems. Read more here.