Hanzhong guard Zhang Lu once said: "I would rather be a slave for Duke Cao than a guest for Liu Bei." As we all know, Liu Bei is a well-known wise master who knows people well, makes good use of them, and treats virtuous subordinates well. There are many talented people under his command, including the Crouching Dragon and Phoenix Infant in literature and the Five Tiger Generals in military affairs. So why does Zhang Lu hate Liu Bei so much? The reasons are simply the following: first, Liu Bei and Cao Cao showed completely opposite attitudes towards the Five Pecks of Rice religion that Zhang Lu believed in; secondly, Cao Cao's military power was superior to Liu Bei's at that time. Zhang Lu was also a man who could adapt to the changing circumstances. He weighed the pros and cons between Cao Cao and Liu Bei, and finally decided to place his bet on Cao Cao's side.

Zhang Lu has been stationed in Hanzhong for many years and has always believed in the Five Pecks of Rice religion. There are many believers in Hanzhong and even Bashu. Zhuge Liang believed in Legalism, and both Liu Bei and Zhuge Liang were disgusted with the Five Pecks of Rice religion. This disgust was also due to the concerns of the ruling class. Because religion as a superstructure has a great influence on people's thoughts, Liu Bei suppressed these religions in many ways in order to better rule the land of Bashu. Zhuge Liang strictly followed measures to suppress the Five Dou Rice Sect. By the middle of the Shu Han Dynasty, the number of believers who believed in the Five Pecks of Rice Religion was very small. Zhang Lu naturally hated Liu Bei deeply. Compared with Liu Bei, Cao Cao's attitude towards the Five Dou Rice Cult was much gentler. According to research, Cao Cao's grandfather, Cao Teng, believed in Taoism (that is, the Five Dou Rice Religion). The important reason why Cao Cao supported the Five Dou Rice Religion was to use the power of religion to win the hearts of the people and lay a solid mass foundation for himself to conquer the world.

As the saying goes: "A good bird chooses a tree to roost in". When Zhang Lu chose to seek refuge with Cao Cao, he also made a careful assessment of the situation. At that time, although Liu Bei was known as the Ming Lord, he lost to Cao Cao in terms of military strength. Zhang Lu had been guarding Hanzhong for many years. Although he had no obvious achievements, he was not an incompetent person. He also wanted to join a powerful camp to ensure that he would be able to flourish and shine in the future. Therefore, he finally chose to surrender to Cao Cao.

Zhang Lu and Liu Bei actually disliked each other. Liu Bei didn't really value Zhang Lu. He recruited Zhang Lu because he valued the territory in Hanzhong, not Zhang Lu himself.