It can be soooo frustrating at times, but when you move beyond a difficult area and realize that you just improved as an artist, right then and there, it's worth it! I may have to try 20 different things to get a nose to look right, or a skin texture to look right, but all that matters is that ONE time it works. Even creating something cartoony or comic-book like can be so fulfilling. It doesn't have to be a huge, epic piece of work.
What kind of FEELING does it give you that is so rewarding?