I think I may have felt this once or twice in my career. I'm 15 years in now. I study type theory and use formal mathematics to model software systems. I don't

I think I may have felt this once or twice in my career. I'm 15 years in now. I study type theory and use formal mathematics to model software systems. I don't have any degrees. In my day job I lead teams writing mostly Javascript to build web services and APIs for moving data around. I teach a small group Haskell once a week at lunch. I speak at conferences big and small. I still wonder at times if I know what I'm doing or whether I deserve to have opinions about anything or blah blah blah. It doesn't help having voices around you all the time that call your skills, experience, and knowledge into question. You have provided value to someone if you're still a practicing software developer. You know how to work in a team, solve problems, and have developed a sense of taste for what problems are worth solving. You understand the tools you use and have an intuition for their strengths and weaknesses. Maybe you even have some experience getting other developers to work together on a large project. That's useful stuff. You are a useful person. Does learning theory help? I think so. Once I stuck with type theory I started to see structure and abstractions in code I couldn't before. Learning how to formalize programs has allowed me to think about the correctness of complex systems in precise ways in order to discover "bugs" in my designs. These have also helped me find more ways to write simple, reliable code.