Martha Graham (1894 - 1991), the American dancer, who created a movement language based upon the expressive capacity of the human body, is quoted as saying something I have often thought but ne'er so well expressed. Read it when you need to dispel the demons of self-doubt, feelings of inadequacy and the sense of futility about one's work that most writers seem to visit at some time - it acts as a kind of charm against them:
There is a vitality, a life force, an energy, a quickening, that is translated through you into action, and because there is only one of you in all time, this expression is unique, and if you block it it will never exist through any other medium and be lost; the world will not have it. It is not your business to determine how good it is, nor how valuable, nor how it compares with other expressions, it is your business to keep it yours clearly and directly to keep the channel open. You do not even have to believe in yourself or your work, you have to keep open and aware directly to the urge that motivates you. Keep the channel open...
(As told by Agnes de Mille in Martha: The Life and Work of Martha Graham. A Biography.)
And this is helpful too:
Practice means to perform over and over again in the face of all obstacles, some act of vision, of faith, of desire. Practice is a means of inviting the perfection desired.