It sucks that you're feeling this but it's an internal thing if that helps. By that I mean you are a failure in your eyes rather than being considered a failure by others. I understand first hand how that may not help much. There is a quote attributed to Einstein that states everybody is a genius but if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid. I don't know if he really said that but there is something to it. It may be all about finding your talent... the niche where your gifts fit. It may not match up to your interests.