"What you get from paper is superficial, and you never know what you have to do", which embodies the following principles of Marxist epistemology:

1. Rational knowledge should be turned into practice. What you get on paper is rational knowledge after all. As far as the understanding of specific things is concerned, the process of understanding is not over yet. It is more important to apply rational knowledge to practice, guide practice, accept the test of practice, and then develop knowledge in practice. Human cognition is such an infinite development process of "cognition-practice-cognition-practice ……".

2. The principle of dialectical relationship between practice and cognition. People's correct understanding of things needs to be further applied to practice. Practice is the power and source of knowledge.

3. Practice is the only criterion for testing truth. The only criterion for the correctness of rational knowledge is practice, and only in practice can we make a correct truth evaluation of the acquired rational knowledge.