We all have one, sadly, I have two. Though I don't think I want to tell you one of them, you might use it against me one day. But I will gladly tell you the other. Writing/new story ideas, I tend to get at least a new idea for a story once a week, even sometimes get two new ideas in a day. Just depends on where my mind wanders off. I try not to wander off from my main story but sometimes you just have too.
Just saturday, I got a new idea inspired by the t.v series Touched by an Angel, which I truly adore now even got a little teary eyed from a few episodes. So of course the idea involves angels, though that whole entire day I wanted to work on it, start writing...I couldn't. If I started it, it would only take my time away from my main story and since I'm so close to finishing I couldn't risk it.
However I have everything I need up in my mind so when I'm ready I can get started.