You know how it is: you have an idea, and it sounds brilliant, so you write it down because, damn, man, this is the one. This is the one. And then, somehow, it never quite pans out that way. The zag never matches up with the zig. The yang never quite lives up to the ying. Or the zag and the yang elope when your back is turned, and there you are, propping up the end of a bar with poor, bereft zig and ying, bemoaning what could have been.
Or, you know, you just have an idea for a title and the story never quite comes.