A funny image I saw on Facebook a few weeks ago went something like this.
Driving to work - Comes up with perfect plot
At lunch break - Comes up with perfect characters
Driving home - Comes up with an amazing ending
Sits at keyboard - whut are werds?
I think just about everyone has gone through that at some point.
Many of my stories were written in a stream of consciousness manner and then edited later. I tend to self-edit brutally - the kind of scene that took place in my head might not be the same as the one I wrote down. What makes sense to me probably wouldn't make nearly as much sense to someone else, especially if they aren't familiar with the particular show or concept that I happen to be writing about.
A great many of my ideas don't even make it into finished stories at all because they're simply too far-fetched to be believable. I have many notebooks and text files filled with plots, scenes, and paragraphs that were never expanded upon or posted.
Now if only I can get the drive to continue on that book I wanted to write this year.