How do you overcome your self-doubt as an artist?

To my fellow artists, how do you as an individual deal with the doldrums? How do you get through those dark days when you question your worth and your value as a creative individual. You know, those days you hear a voice that tells you you'll never be good enough, that you'll never be a "professional" or as good as those artists who inspire you. Just figured it'd be nice to share ideas to those who might find it an almost impossible task at times.