How do you measure success? Is it by money or is it by how well you did a task? Or do you compare yourself to someone else? If it is the last one, then you may get hit with envy. Consider, comparing your work to what you have done in the past.
When I look at code I wrote a year ago or even a few months ago, I may cringe. Cringing is a good thing. That means I have improved. I can look objectively at code and critique it. If I can critique it, I can improve it.
Think about art in the same way. Keep some of your earlier pieces to see how far you have become. It may not even be a progress of a certain art technique. You may see how far your art style have changed. Is it from realism to abstract? Or is it from tight to loose work of art? Only you can evaluate your own success.