I followa very simple logic where my writing is concerned, if it strikes me as a fun thing that just grabs my attention from beginning to end (regardless how many revisions I make) I run with it. If it doesn't grab my imagination after 5,000 words than I call it quits.
Thus far, Enemy Within and Ghost of Missions Past are keeping me focused. Then again, so is a previous story featuring my main character and corporate ran refugee centres. More on that later . . .