I caught this smart little video from The School of Life. It tells the story of a little character who is looking to create his own masterpiece. In his minds eye he can see it, this this thing of beauty, his crowning glory... his moon shot accomplished. But, of course, like any creative process, the reality of his first draft is a million miles from the vision he had set out to fulfill. The narrator talks about despair being cheap and that horrible feeling of your own profound mediocrity.
Bottom line is, for literally everyone, it never goes the way you expect... accepting this is half the battle. Passion and persistence (and all of your other wonderful attributes) will get you there though.