Why was it said that the opening and ending of the Four Great Classics hid a big secret? What secret was it exactly?

The opening and ending of the four masterpieces all hid a big secret. This secret was an important information and event about Chinese history and culture. At the beginning of 'Dream of the Red Chamber', the author Cao Xueqin described the life of a wealthy family and hinted at the fate and background of these characters. Through the story of this family, the author conveyed some important information, such as the corruption and decline of China's feudal society and the complexity and contradiction of human nature. This information was very important for understanding the theme and plot of the novel. At the end of Journey to the West, the author Wu Chengen described the scene of Sun Wukong and other characters defeating the demons, and also hinted at some important information such as the politics and culture of the Tang Dynasty. This information helps the reader understand the background and historical background of the novel. At the beginning of Water Margins, the author Shi Naian described the lives and fates of a group of righteous thieves and conveyed some important social messages through these characters 'stories, such as social injustice and the importance of justice. At the end of Romance of the Three Kingdoms, the author Luo Guanzhong described the history and characters of the Three Kingdoms period, but also hinted at some important information such as the selfishness of human nature and the pursuit of interests. This information helps readers understand the theme and plot of the novel. Therefore, the beginning and the end of the four masterpieces hide important information and historical events, which are very important for understanding Chinese history and culture, as well as important aspects of human nature.