A good cook changes his knife once a year because he cuts. A mediocre cook changes his knife once a month because he hacks. I've had this knife of mine for nineteen years and I've cut up thousands of oxen with it, and yet the blade is as good as though it had just come out of the grindstone. There are spaces between the joints, and the blade of the knife has really no thickness. If you insert what has no thickness into such spaces, then there's plenty of room - more than enough for the blade to play about it. That's why after nineteen years the blade of my knife is still as good as when it first came from the grindstone.
— Zhuangzi: Basic Writings