I always feel like such a flake when that happens ... I don't like to come off as some sort of prima donna, and really it annoys me when art is treated as some sort of amazing thing that comes floating down out of the sky and the artist just happens to be the conduit for it. At some fundamental level, art really consists of doing nothing more magical than rubbing the tip of a pencil against a piece of paper so that it leaves a series of smudges that our mental processes read as a picture.
I think some of it may be that my artistic ego is getting in the way. I know that on at least one of these pieces, the reason it isn't going anywhere is because I've done the subject so many times that I've run out of ways to put a new spin on it -- and my ego says that if I can't come up with something clever to do with it, I shouldn't do it at all.
Maybe I should cruise Yerf or something looking for ideas to steal ... that might at least give me enough of a spark to get things moving again.
PS: And in case you're wondering, "Hey, aren't you at work?" the answer is: yes, I am. Most of my best work is done when I should be doing something else. Le sigh.