There's alot of times when I'll work on some artwork or graphics and spend hours upon hours tweaking and fixing things only to delete it all and revert back to a previous "more simple" version of it. Less is more - simple is easy to translate and (if done right) makes more of an impact because the message is clear.
I moved into the realm of confusing with the colors for this comic. I cranked it up to 11, but it was too busy and ugly. What should have been grass became an eyesore, drawing attention away from the meat of the panel. So I went back (again) and turned the volume down.
I didn't know when to stop coloring, but I think I do now. The same goes for everything - when to stop writing a guitar riff, a story, song lyrics, when to stop a design, an illustration, and most importantly, when to stop planning.
You can plan forever, but it's only when you start moving that great things happen.