I enjoy metaphors. I feel they help put things in perspective like...well, you get what I am driving out. So its hardly surprising I have a metaphor I drag out whenever I am asked to explain my view on what a Dom/sub relationship is like.
As the title hints I compare it to the creation of art, specifically a painting. Two things are necessary a painter, the Dominant, and a canvas, the submissive. Without the other one is unfinished and the other is a crazy, starving figure smeared with odd streaks of color and possessed of a tenuous grasp on reality. Together they can create something wonderful and timeless. It may seems the painter has all the power, that they can simply impose their vision on the canvas but its not true. The boundaries of the canvas define the limits of that visions and its composition guides what kinds of paints can be successfully applied. It is only with full and harmonious understanding on both parts that anything good can come.
Not exactly perfect, but I think it covers the basics quite well.