How do I stay focused on one game idea? Options

[Pinky]

I'm not really sure where to ask this, I am asking more for help on staying focused on one game idea.
It's seems like every time I start on a game and release a demo I have trouble keeping interest and staying focused on it and then end up with a bunch of unfinished demos which you guys and girls here probably noticed. How can I stay focused on one game idea and keep the game going with improvments? How do you guys and girls manage to do that?