You need to develop not only the writing muscle but the finishing muscle. ANYONE can write thirty pages (and as we've seen...they will). But finishing the thing and putting in the effort to make it a coherent, complete beast is a different skill set and one you need to work on.
Seriously, this was my biggest problem for the longest time. I would work on something and then say, "Well, but there's this problem, and this..." and then I would move on to the new shiny. And do it again.
Learning to finish has been the biggest difference.