we spend more time understanding where we went wrong, rather than working out what we did right
That's because when you know where you went wrong and avoid doing that and everything now looks right then you're right XP
Though as far as I can tell even the writers and artists I know that put out amazing stuff that their viewers deem flawless still see everything that went wrong from that misweighted line to the wrong shade of black, or in the case of writers that one word repeated slightly too many times or that sentence that could have been that little bit tighter or that description that could have been that little bit more show than tell xD
I wonder if we explored the stuff we dd right, if we would realize there was a lot more we could have done.
Artists are a different breed in many respects - perhaps art is about expressing an opinion of some sort and the artist can recognize the disconnect, even if the viewer can't?
Actually now that you mention it I think that a lot of the good artsts probably are analysing what they did right (which could be how they find everything they did wrong in that right even if no one else can see it).
Actually I really think artists (including writers, musicians etc) just have on average a higher chance of some kind of clinical depressive thing and/or low self esteem which then naturally inclines them to being overly critical of themselves XD