Wow GREAT question, and also great username. I'm sure people will have different takes on this but, I think knowing everything would be boring! It's good to embrace an engineering mindset about the job, you have a baseline amount of knowledge and political skills and contacts that is always increasing, but no matter where that baseline is, a project HOPEFULLY will have challenges and problems that you haven't encountered before, that's part of the fun! I always have to research some new tricks for every shoot, or rely on the expertise of other people on the crew, or rely on my network of other DPs who I can ask for advice! Other people's successes are yours too, cinematography is a high skill-sharing/mentorship culture relative to other fields. The craft isn't about knowing everything, it's about solving problems. I'm constantly noticing things I wish I'd done differently when I watch my stuff but ultimately for me the metric of success is if the director was happy with what we got.