Reading The Essential Interviews edited by Jonathan Cott. Happened across this:
Well, first of all, anybody that’s got a message is going to learn from experience that they can’t put it into a song. I mean it’s just not going to come out the same message. After one or two of these unsuccessful attempts, one realises that his resultant message which is not even the same message he thought up and began with, he’s now got to stick by it; because, after all, a song leaves your mouth just as soon as it leaves your hands. You’ve got to respect other people’s right to also have a message themselves.
Replace “song” with “ad” and Robert Zimmerman is your father’s brother.