During the Three Kingdoms period, a famous battle known as the Battle of Red Cliffs took place. Cao Cao, leading an army of a million, intended to conquer the south. The states of Wu and Shu formed an alliance to resist Wei.

Zhou Yu, the commander of Wu, and Zhuge Liang, the strategist of Shu, together devised a plan to attack Cao Cao. They decided to use a fire attack, exploiting Cao Cao's arrogance and underestimation of his enemies. First, Zhou Yu employed a counter-espionage scheme, tricking Cao Cao into killing his skilled naval generals, Cai Mao and Zhang Yun, who were familiar with water warfare.

Next, Pang Tong pretended to offer advice, deceiving Cao Cao into linking all his warships together. This arrangement would ensure that if a fire broke out, the ships could not be separated, leading to the complete annihilation of Cao Cao's forces. Zhou Yu then staged a 'bitter trick,' publicly flogging the veteran general Huang Gai, who then feigned surrender to Cao Cao. In reality, Huang Gai's ships were filled with combustible materials, ready to charge into Cao Cao's camp during the false surrender and launch the fire attack.

Everything was meticulously arranged, yet Zhou Yu was not happy; instead, he fell ill with worry and was confined to bed. The reason was that a crucial condition for the fire attack was still missing: to set fire to Cao Cao's camp on the north bank, a strong southeast wind was essential. However, it was deep winter, and the prevailing winds were always from the northwest.

Zhuge Liang visited Zhou Yu, who eagerly asked for a solution. Zhuge Liang told Zhou Yu that he could summon the wind and would call for a southeast wind for three days and three nights to aid Zhou Yu's fire attack. Zhou Yu immediately ordered the construction of an earthen altar, called the 'Seven-Star Altar.' Zhuge Liang then performed rituals on the altar to pray for the southeast wind. Zhuge Liang, with his profound knowledge of astronomy and geography, had observed the weather patterns and predicted the exact date when the southeast wind would blow.

On the appointed day, a strong southeast wind indeed arose, allowing Zhou Yu to successfully carry out his fire attack plan. This story gave rise to the idiom 'Everything is ready, only an east wind is lacking,' which is used to describe a situation where all preparations are complete, and only the last crucial condition is missing.