Curb your enthusiasm

There is now a creative and funny program on a cable channel in the states called "Curb Your Enthusiasm". The title phrase is one I've heard all my life, with no sense of its origin or history. Can anyone help?
I can remember hearing, "Curb your tongue, knave!" In other words, "Be quiet!" or "Shut up!"

There is also the gentle reminder to, "Curb your dog!" meaning "Please have your dog do its business at the side of the road."

I am unsure of its origin.