One reason some budding authors never fully bud is because they expect their writing to be polished upon the first keystroke.
However, as Kevin Ashton, the author of the Amazon Editors' Pick How to Fly a Horse: The Secret History of Creation, Invention, and Discovery, related, it takes a number of revisions, erasures and rearrangements before writing can shine.
Nothing begins good, but everything good begins. Everything can be revised, erased, or rearranged later. The courage of creation is making bad beginnings.
But as Terry Pratchett advised, DON'T start doing any editing until AFTER your brain dump (i.e., first draft.)