Another thing I heard in the documentary about Woody Guthrie was Arlo Guthrie saying that Woody was always writing. If there was any piece of paper in the home, he would write on it. If he went to someone's house, he'd write all over whatever paper they had in their house. If there was toilet paper, he'd put it through the typewriter, and then he'd turn it over to the other side and put it through again.
In a way, I can relate. I'm not as prolific, I use the computer rather than paper, and I don't write lyrics, but still, I have the compulsion to write. The words well up inside me and demand to be written.