When I finished my first novel, I gave it to my husband to read and asked, "Does it seem like a real book?"
It seemed like an actual book with a plot and characters. More or less -- I was aware that there was something that was NOT like a book about it -- or not like the kind of book I wanted to write. I had created a complex community, huge cast of characters, and an original magic system and grafted it onto a lot of historical research. In my inexperienced hands, the story felt kluged together with rubber cement and cellophane tape. There was a huge gap between my vision and my execution.
In the end, after revision, that manuscript was enough like a book that I got an agent, but not enough that we managed to sell it.
For my next project, I aimed to write a book with a scope I could manage -- I set it more or less in my own backyard. That book turned out to be Deadwood -- and although it got published, there was still a gap between what I wanted to achieve and what I accomplished creatively.
The book I'm working on now is a story I put off for years because I knew I couldn't do it justice. Then eventually I started writing because whether I achieve my vision of what I want or not, it's the kind of story I want to read. The only way to read this particular one is to write it, whether it ends up published or not.
There will always be a gap between what I want to write and what actually shows up on the page, but being too conscious of that gap means I won't cross it. Instead, I'm going to fill it with words and maybe find myself on the other side.