True art, said Einstein, is characterised by an irresistible urge in the creative artist. The urge to create, to let it flow out: like children dancing or drunken wedding guests singing. There's no rhyme, there's no reason. It just comes tumbling down.
Art, like dreaming, is a way for the soul, the mind of man, to make sense of the world. According to Aristotle filling in the gaps in nature; according to Chagall trying to improve on nature, but failing.