In one of my art classes, I was told that Michelangelo was such a good artist, he could freehand a perfect circle. I haven't checked sources on this, but I told this to my nine-year-old nephew one day. His response? "I can do that. That's easy."
"Remember," I said, "just because something is simple and you understand how to do it, doesn't make it easy."
My nephew pulled out some paper and a pencil and got to work. One thing I want to say. . .generally speaking, he's not a very patient person. He likes to get stuff done as fast as possible. So I knew this would be interesting.
He drew circle after circle after circle (rather quickly considering it needed to be perfect.) After about 15 minutes, he said, "I can't do it."
Just because something is simple and you understand how to do it, doesn't make it easy.
Earlier I talked about your writing eye, and how it should, hopefully, be ahead of your abilities. Understanding and knowing how to do something is the first step, but it can take lots of practice to do it right. I think sometimes we forget about this with writing. I know several people who have an amazing eye for writing, but then I read their work and was surprised to see that they couldn't yet follow their own advice. They're still learning. And we should all still be learning.
Their insights reveal their potential for where they can be.