Secondly, not only the history of China, but also the leaders of all countries in the world operate behind closed doors when formulating policies. Most ancient historians in China are very strict, but the compilation of history can only be done after the demise of a dynasty. Many things that happened before have always been a mystery, and future generations have not experienced those events personally, so they can only write according to existing materials.
Also, when a ruler is alive, he can't read his own great works, but some people can read them, such as Li Shimin and Emperor Taizong, who often threaten to correct his wrong words and deeds, so there are always mysteries in history.
Finally, the war broke out and books were compiled, which led to the frequent destruction of books. Qianlong ordered Ji Xiaolan to compile Sikuquanshu, which was called the second cultural catastrophe in China. The first time was to burn books and bury Confucianism, and the third time was the Cultural Revolution. However, when Jie Jin was sent by Emperor Cheng Zu of the Ming Dynasty to compile Yongle Dadian, Judy accepted it completely and didn't burn it.