Liu Bei was a good soldier. Why didn't he win the world championship in the end?

As far as the Romance of the Three Kingdoms is concerned, Mr. Shui Jing told Liu Bei that Wolong Feng Chu could win the world by himself. This is only an affirmation of Wolong Feng Chu's ability, not a fortune-teller saying that with Wolong Feng Chu, the world can be unified; What's more, Pang Tong hung on the Phoenix Slope before he could fight. Guan Yu did not carry out Zhuge Liang's major policy of uniting with Wu to resist Cao. Not only did he lose Jingzhou, a strategic place, but Guan Yu himself died, and Zhang Fei and Liu Bei who were involved in the incident also died one after another. Of course, this does not unify the world.