The definition of contentment is that people should not always be extravagant, but should know how to satisfy what they have; Lack of knowledge means that you don't know what your goal is and what you want to achieve through hard work, mainly referring to your shortcomings as a person. Simply put, you should be self-aware. Doing something and not doing something refers to what can be done, what must be done and what cannot be done. We should have our own principles and stick to them.

"Lack of knowledge" is manifested in positive and enterprising spirit, strong desire for knowledge and modest and studious attitude. Make continuous progress in study and career, and never be satisfied. In the bottom line, "promising" means doing something.

The source of "lack of knowledge" comes from the Book of Rites: "Learn and then know the lack, … know the lack, and then you can defeat yourself."

Only by studying can we understand our own shortcomings and know our own shortcomings, and then we can study hard in turn. )

Extended data:

The creative background of Xue Ji;

The Book of Learning is one of the Book of Rites, which was written from the 4th century BC to the 3rd century BC. According to Guo Moruo's textual research, its author may be Ke, a student of Mencius.

Gu Shusen supported Guo Moruo's view that Xue Ji was written by Le Zhengzi, a Confucian scholar, at the end of the Warring States Period, and borrowed ideas from the school, probably by Ke, a disciple of Mencius. Gao Shiliang also agrees with this view, thinking that Xueji is a work of the Warring States period, and the specific time is in the late Warring States period.

Its author should be Ke, because Ke is Mencius' favorite pupil and deeply influenced by Mencius' thought. Secondly, Le Zhengzi also studied under Zeng Shen, "Le Zhengzi said that I had heard of Ceng Zi". Third, the original music is a scholar, and the Book of Rites says:' Music is advocating four skills and establishing four religions. The descendants of academic officials all have family origins in education. "