In the hemp plant, if you don't help yourself to be straight, the white sand is in nirvana, which means that Peng grew up in the hemp field before, so he is naturally straight and doesn't need help. White fine sand mixed with black soil will turn black. It is a metaphor for living in a good environment and getting healthy growth. For example, a good person or a good thing in a polluted environment will also deteriorate with the polluted environment.

From Xunzi's persuasion, used to persuade students. Whether philosophers or ordinary farmers say this sentence, they all express the great influence of the environment on plants and people. Metaphor in a good environment, will naturally get healthy growth. The full text consists of two parts: the first part discusses the importance of learning; The second part discusses the steps, contents and methods of learning. And "learning can't" is the central idea that runs through the whole paper.