"A skillful craftsman knows an ox" is an allegorical story created by Zhuangzi, a representative of Taoism in the pre-Qin period. The author's original intention is to explain the way of keeping in good health, thus revealing the truth that people should conform to the laws of nature when doing things. This fable is intended to illustrate health preservation, in fact, it also expounds a profound aesthetic proposition, that is, artistic creation is a free creation. So it's not just a technical problem.