In my opinion, one can never ever know all there is to know about any topic. But there will always be someone who knows more, or knows something different. There is always learning to be done. Things constantly change and evolve and no one can ever be all-knowing about anything.
And this is a great thing :)
When I started writing, just like starting anything else, I knew very little. I did what I could on my own, what my instincts told me, and then went to my number one resource for learning anything and everything these days: the internet! I learned a lot and soaked it up. But there was a lot of conflicting info out there. And that's bound to happen with anything. But then I started meeting people....other writers in the same boat as I was. We learned together, shared information, figured some things out together. We took the resources available to us from reliable sources who'd been where we were and were nice enough to share what they'd learned.
And then I came to a point where I could start helping others who were not as far along in the journey as I was. And that felt great! I knew I was no where near a point of knowing everything, but I could help. I could share what I had learned along the way. Point someone else in the direction they needed to go.
I'm in a great place these days, but I still need to learn more. I still turn to those farther along than me. I turn to the best! There are so many wonderful authors out there who seem to have it all going on. I read their books, study their methods, learn what I need to do next. Keep moving forward.
I know I'll never know everything and that's okay. But there will always be people ahead of me to learn from. I only hope they know how thankful I am they are there to guide me. And I hope to be a good role model for those not yet in the place I am :)