Friends who know the history of the Tang Dynasty know that Li Dan of Tang Ruizong became emperor for the second time by relying on the support of his sister Princess Taiping and his son Li Longji. According to the reason = general common sense, Tang Ruizong Li Dan should be treated equally after he ascended the throne, and his support for Princess Taiping and Li Longji should be similar, and he should definitely be closer to his son than his sister.
When Li Dan first ascended the throne, he did treat Princess Taiping and Li Longji equally, but in the next few years, Li Dan began to clearly support Princess Taiping and suppress Li Longji. This somewhat eccentric support tendency reached its peak after Li Dan took the initiative to abdicate the throne, and finally let Li Dan pass the "addiction" of Tang Gaozu Li Yuan. So why should Li Dan favor one over the other?
According to the clues recorded in the history books, it can be found that neither Princess Taiping nor Li Longji really supported Li Dan as emperor. His son Li Longji was particularly unsincere, and when he eliminated empress Wei's clique, he once hinted that his subordinates supported his ascension to the throne. Because the conditions were indeed insufficient at that time, Li Longji supported his father as emperor in exchange for his father appointing him as crown prince.
Li Dan is well aware of his son Li Longji's ambitions. What makes Li Dan even more uncomfortable is that Li Longji's talent is almost all-round beyond his father. In addition, the position of crown prince gave Li Longji the legitimacy to participate in imperial politics and inherit the throne, and many important ministers and celebrities represented by Yao Chong, Song Jing, supported the crown prince Li Longji instead of emperor Li Dan.
It can be said that Li Dan and Li Longji are the "low-grade versions" of Tang Gaozu and Tang Taizong, and the person who threatens Li Dan's imperial power the most is his own son Li Longji. In order to balance Li Longji, who aspired to the throne and was highly respected, Li Dan supported his sister Princess Taiping to fight with him. As a result, Li Longji became more and more dissatisfied with his father, and Princess Taiping's ambitions became more and more inflated.
In order to balance his sister and son, Li Dan came up with a seemingly clever method: cede the throne to Li Longji, and he himself became the emperor to control the supreme power and rely on his sister to control the government, resulting in Li Longji's power shrinking after becoming emperor. Li Dan's forcible separation of imperial power from the emperor could only create greater contradictions, which eventually triggered an "innate coup".