I've always felt that focus was a challenge for me. Not in terms of concentrating on the task at hand; I'm good at that. I can sit and write for hours on end. But in terms of picking one task and staying with it through to completion. Part of it is that I'm interested in so many things that it is easy to get distracted with something else. Similarly, I have so many stories bumping around in my head that want to be told, it seems like just when I start to sink my teeth into one, another one pops up demanding time and attention.
That and I decided some time ago that a good career move would be to write some short stories along with the longer stuff I was doing. Only problem... the short stuff keeps turning out to have more plot to it than I can squeeze into a short. But, having been envisioned as a short, they usualy don't have enough to make it quite to a full novel.
So now I've got six works in progress all of which could be novel length, and I have to try and focus on one or two. I suppose it is as much a discipline problem as it is a focus problem -- it takes discipline to stick with the one story and not go off chasing other stories that are equally interesting.
And, of course, the new story has the allure of being new, the excitement of dreaming up new characters and new plot twists, rather than just writing out what you've already plotted out (or having to plot yourself out of corners you've written yourself into!).
Anyway, I think at the next con I go to I'm going to ask the pros -- how do you decide which project to go with, and how do you stick to it once you've chosen?