Indigo is extracted from indigo plants, but it is bluer than the plants from which it comes.

Xunzi, whose real name was Xun Kuang, was also known as a native of Zhao in the Warring States Period. He was a famous materialist thinker and an outstanding representative of the ideological circle during the Spring and Autumn Period and the Warring States Period. He kept all his life's research achievements in Xunzi, which systematically reflected his philosophy, education and political thoughts. His educational thought still has reference significance today.

"Encouraging learning" is the first of the thirty-two articles in Xunzi. In this article, the author comprehensively discusses the purpose, significance, attitude and methods of learning, which has profound enlightenment to people. There is such a passage in the article: "You can't teach yourself. Green is taken from blue, and green is blue; Ice is made of water, but it is cooler than water. " Learning should not stop and give up. Cyan is extracted from blue dye, but it is bluer than blue; Ice is made of water, but it is colder than water.

Here, Xunzi uses the metaphor of the relationship between blue and green, ice and water to show that students can improve as long as they study hard and persevere. Students must be more ambitious than teachers, and each generation is stronger than the next.

The famous saying "shine on you is better than blue" was first said by Xunzi.

Later, these words evolved into the proverb "shine on you is better than blue", which is used to describe that students are better than teachers, and future generations are better than the former.