Yao and Zhu's difficult books can also refer to fine arts, which are difficult to copy and imitate. In the ancient art of China, especially in the traditional art fields such as silk, porcelain, calligraphy and painting, there are many exquisite works by Yao and Zhu, which are the cultural treasures of China and have immeasurable appreciation value and historical value.
Yao Zhu's difficult book can also refer to secrets or secrets that will never be easily revealed. This kind of secret is usually important and confidential information or documents, and only specially authorized personnel have the right to consult and handle it. In modern society, secrecy has been paid more and more attention, and Yao and Zhu's concept of hard pen has also extended to the field of secrecy to a certain extent. It has extremely high practical value and safety benefits.