Wasn't sure where to post this, but I read this today, in an article called Writing Without a Plan, and it helped me.
"For me, the page is all I get, and the page is what makes the soup of the mind into something tangible. If there is no book in my mind, then the only way I can find a book is by writing it. This act of writing is how I get access to the material I might not readily know about. We cannot read each other’s minds, and the truth is, we often cannot really read our own.
There’s something sad in this—that we cannot replicate our idea, our perfect, imagined book in there, our brilliant ideas that seem so full and glorious when walking past the autumn leaves. But the amazing side, the truly amazing side, is that we might write something else, something surprising."
Here's the whole article. https://lithub.com/aimee-bender-on-writing-without-a-plan/