Habits and their Consequences

I have a problem. I'm a very imaginative, artistic person, however everything that catches my attention can completely throw me off what I was working on. I must have eight stories that never grew past the first two pages, all of which could have been good works of fiction if I could just have focused better. Even now, I've considered writing a story simply by playing a card game and hearing a good song, yet probably won't due to my record of abandoning projects that barely even start.
The ONE story that I've actually published on this site was one of my first stories, and I lost all track of where I was bringing the narrative. of the many fan stories I've attempted to make, nearly one third are acceptable for this site, and I know at least I would adore reading several of them. I only ask, to anyone who might be able to answer, how does one overcome something as artistically crippling as this?