A proud army will lose the battle. In fact, it refers to the story that Guan Yu was blind and self-confident, refused to accept Zhuge Liang's suggestion of "linking Sun Quan in the east and rejecting Cao Cao in the north", and resisted Wu Dong and Cao Wei's two major military groups by himself, and was finally killed.

Introduction to Guan Yu's loss of Jingzhou: After Battle of Red Cliffs, seven counties in Jingzhou were divided by Liu Bei, Cao Cao and Sun Quan, and Liu Bei entered Sichuan, leaving Guan Yu to guard five counties in Jingzhou (Nanjun, Changsha, Lingling, Guiyang and Wuling), of which Nanjun was borrowed from Wu Dong by Liu Bei. After Liu Bei got Shuchuan, he returned Changsha and Guiyang counties to Sun Quan (equivalent to returning Nanjun).

Later, Guan Yu sent troops to attack Cao Cao's Xiangfan area, and Sun Quan sent Lu Meng to attack the fall of three counties in Jingzhou (Nanjun, Wuling and Lingling), which led to the fall of three counties in Jingzhou. Careless loss of Jingzhou is now a metaphor for failure or loss caused by negligence, which means carelessness, pride and underestimation of the enemy.

Extended information Guan Yu's original word is immortal, and later it was changed to Yun Chang. In his early years, he fled his hometown to Zhuo Jun County (now Zhuozhou City, Hebei Province) because of crimes. ?

In the first year of Zhong Ping (184), Liu Bei, a relative of the Han clan, organized a volunteer army in Zhuoxian to fight against the Yellow Scarf Army, and Guan Yu and Zhang Fei were among them. After Liu Bei was transferred to many official posts, he defected to his former classmate Gongsun Zan, sealed Ping Yuanjun, and appointed Guan Yu and Zhang Fei as other ministries, and enfeoffed different ministries. Three people are brothers and often sleep in the same bed. After Liu Bei was seated, Guan and Zhang took good care of him.

After Battle of Red Cliffs, Liu Bei helped Zhou Yu of Wu Dong attack Coss of the Southern Army, so he didn't send Guan Yu to the North Road to stop Cao Cao's reinforcements. After Coss retreated, Guan Yu was appointed as the prefect of Xiangyang by Liu Bei. Liu Beijin Yizhou, Guan Yu stayed in Jingzhou. ?

In the twenty-fourth year of Jian 'an, Guan Yu surrounded Xiangfan, and Cao Cao sent reinforcements. Guan Yu captured Yu Jin alive and killed Pound, which greatly shocked China. Cao Cao wants to move the capital to avoid its sharpness. Later, Cao Cao sent Huang Xu to reinforce, and Monroe of Soochow attacked Jingzhou. Guan Yu was caught between Scylla and Charybdis and was defeated and killed.

References:

Baidu encyclopedia-Guan Yu