Li Yiji was a strategist under Liu Bang, the King of Han, who had lived in poverty until he joined Liu Bang's service in his sixties.
Li Yiji became Liu Bang's trusted strategist, guiding him to capture Chenliu and secure ample military supplies. Li Yiji's brother, Li Shang, also rallied 4,000 men to join Liu Bang, rising to become a general. From then on, Liu Bang placed great trust in Li Yiji, appointing him Lord of Guangye.
After the Qin Dynasty fell, Liu Bang and the hegemon Xiang Yu fought for control of the realm. Xiang Yu's military might was overwhelming; at the Battle of Pengcheng, Liu Bang's forces suffered devastating losses, forcing him to retreat and shift from offense to defense. Falling back to Xingyang and Chenggao, Liu Bang relied on the strategic advantage of mountains and rivers—where he could advance to attack or retreat to defend—leaving Xiang Yu's Chu army momentarily at a loss.
However, the Han army's food supplies were also running low. On Mount Ao, northwest of Xingyang, stood a small city built during the Qin Dynasty, filled with grain storage warehouses, hence called the Ao Granary. As the largest granary east of the Hangu Pass, it held all the grain shipped from the Jianghuai region and Shandong, making its capture crucial for the war effort.
Xiang Yu's fierce assault left Xingyang on the brink of collapse, as the armies of Chu and Han clashed bitterly in the region, locked in a stalemate. Liu Bang's remaining Han forces were also embroiled in intense battles elsewhere, unable to send reinforcements.
With no other viable option, Liu Bang planned to cede the land east of Chenggao to Xiang Yu and retreat to the Gong and Luo regions, hoping to catch his breath and reorganize his forces for a decisive battle against the Chu army.
Li Yiji learned of Liu Bang's plan and objected, saying, "A ruler relies on the people as his support, and the people rely on grain. Aocang is a vital granary rich in stored food, yet you, Great King, want to abandon it. Losing such a favorable granary will cause great harm to the army!"
Liu Bang pondered for a moment, found Li Yiji's words reasonable, and quickly asked, "Then, in your esteemed opinion, what should I do?" Li Yiji replied, "In this situation, you must not retreat. Your Majesty can only organize forces to hold Xingyang, protect Aocang, and ensure ample provisions to boost the soldiers' morale."
Liu Bang followed Li Yiji's advice and indeed achieved victory.
Later, people used the idiom "Food is the first necessity of the people" to emphasize the importance of food for the populace.
Source: *Book of Han*, "Biography of Li Yiji"
Meaning of the Idiom: Later, the Chinese idiom "民以食为天" came to describe how food is the first necessity of the people.