This is the Rule of the Gift, which says that if art is your duty, then you must create. The nature of a gift is that it is to be given away, so the first duty of an artist is to do your work. There is a spirit of generosity in every creative act, but to embody this generosity we cannot starve. We must be creating with full bellies and full souls, and so the second duty of an artist is to make money to make art.
