During the reign of Emperor Huan of the Eastern Han Dynasty, the eunuchs wielded enormous power at court.

They not only manipulated the law for their own personal gain, but also ruthlessly persecuted anyone who dared to criticize or oppose them.

In 166 AD, the eunuchs fabricated a case against hundreds of government officials and ordinary people, accusing them of "forming secret cliques and slandering the imperial court." Many of those implicated were subsequently arrested and imprisoned.

When Dou Wu, the father of the empress and an upright and respected official, learned of the case, he decided to submit a formal protest to the emperor.

In his memorial, Dou Wu bitterly condemned the eunuchs' abuses of power and warned Emperor Huan that if he failed to learn from the downfall of Hu Hai, the last emperor of the Qin Dynasty, he might "follow in the footsteps of an overturned cart." Dou Wu went even further. As a man of courage and integrity, he submitted his resignation and vowed that he would never serve in the same court as such corrupt and treacherous eunuchs.

Under mounting pressure from both inside and outside the imperial court, Emperor Huan eventually overturned the case and ordered the release of everyone who had been imprisoned by the eunuchs.

Today, the idiom is used to warn people to learn from the mistakes and failures of others and avoid making the same mistakes themselves.