Rhetorical devices of metaphor. "Book Mountain" and "Learning Sea" are metaphors of knowledge and learning. "Book mountain" means a mountain of books, and "learning the sea" means learning the sea. There is no limit to learning the sea, and there is no limit to learning the mountains, which means that if you want to swim in the boundless ocean of knowledge, a patient and hard-working learning attitude will be a sailing ship that can take you to the other side of success; If you want to reach the summit of the lofty mountain of knowledge successfully, diligence is the only way to reach the summit. This sentence comes from Han Yu, a famous writer and the first of the eight masters in Tang and Song Dynasties. This sentence is included in "Glory and Contribution", which is a famous saying of his scholarship. It aims to encourage people to study more without fear of difficulties, and only hard work can lead to success. Han Yu, whose real name is Tuizhi, is from Tanghe Heyang. Self-proclaimed county king Changli, known as Han Changli in the world. Su Shi, an advocate of the ancient prose movement in Tang Dynasty, called him "the decline of eight generations of literature" in Song Dynasty. Ming people called him the head of the eight masters in Tang and Song Dynasties, and he was also called "Liu Han" with Liu Zongyuan. Known as "a great man of literate Sect" and "a hundred generations of literate Sect", he has written forty volumes of Han Changli's Collection, ten volumes of Waiji, Shi Shuo and so on.