From Hey Whipple Squeeze This:

“Creativity is like washing a pig. It’s messy. It has no rules. No clear beginning, middle or end. It’s kind of a pain in the ass, and when you’re done, you’re not sure if the pig is really clean or even why you were washing a pig in the first place.”

The creative process is basically chaotic at its core and, for me at least, the washing-a-pig metaphor works on several levels.