1. Xunzi: If you don't smell it, if you smell it, if you don't see it, if you see it, if you don't know it, if you know it, you won't do it.

explanation: what you don't hear is not as good as what you hear, what you hear is not as good as what you see, what you see is not as good as what you know, and what you know is not as good as what you do. When learning is done, it will reach the extreme. It means that practice is the only source of knowledge and the only criterion to test the truth of knowledge.

2. Lu You: I have a shallow understanding of what I got on paper, and I know nothing about it.

explanation: after all, the knowledge gained from books is superficial, and you must practice it yourself if you want to know things thoroughly.

3. Li Guangdi: The knowledge of learning is not what you need to know; What you know is not what you do.

explanation: it is better to master the main points than to learn extensively; It is better to put it into practice than to grasp the main points. Show the importance of practical action.