I can see how someone else would--but it's hard for me to relate because I dream of having your talent and everything I could do with it. I wouldn't even consider myself an artist for what little talent I possess. I find it hard to imagine being able to create such beautiful works and not being happy. I know it's just a matter of perspective, though. I'm sure we're probably in similar spots--not being content with what we make. Even if I were at your level, I'd probably look at my art far too critically and be unhappy with it.
I don't think I'm consistent enough with that I produce to really get tired of my art but... I do tend to feel ashamed of the things I've drawn in the past quite fast. I've only recently got comfortable with digital painting, so I'm working on a rather cool painting now (by my standards anyway!). I'm pretty impressed with myself at the moment actually