The subject of "evaluating" one's own art and being thus discouraged is an interesting one. Failure to evaluate at all, for the would-be professional artist, is probably not safe. You are putting your art into a market. It's wise to both know what is expected and what "the competition" is doing. For the beginning artist, however, too much comparison can be stultifying. The beginning artist should practice, practice, practice.Chapter 17 of The Way to Happiness, a secular moral code by L. Ron Hubbard, is very helpful. The precept discussed is Competence. How does one become competent? A pdf version of the book is available at http://www.thepathwaytohappiness.com/. I highly recommend it.