When Emperor Taizu of Song, Zhao Kuangyin, passed away, the throne passed to his younger brother Zhao Guangyi (Emperor Taizong), while his second brother Zhao Tingmei and his own son Zhao Dezhao were given important positions.
Although Tingmei held the powerful posts of Chief Minister of the Secretariat and Mayor of Kaifeng, and was enfeoffed as the Prince of Qi, wielding even greater authority than the prime minister, he was inherently arrogant and willful, repeatedly plotting to usurp the throne. This led to a joint accusation by seventy-four officials, including the Grand Preceptor to the Crown Prince, Wang Pu, who declared that Tingmei's high treason warranted execution.
Emperor Taizong of Song summoned his chief minister Zhao Pu and asked him to explain the matter. Zhao Pu then recounted the entire story from the past in full detail.
In the second year after Zhao Kuangyin became emperor, his mother, Empress Dowager Zhaoxian, fell gravely ill. She asked Zhao Kuangyin, who never left her side, "My son, do you know why you were able to become emperor?" The emperor hesitated, unable to answer. Pressed by his mother, he finally forced out, "Your son gained the empire because of the accumulated virtue of our ancestors and Your Majesty!"
"No!" the Empress Dowager said. "It was Emperor Shizong of Later Zhou who made you emperor. If Later Zhou had a suitable heir, how could the world have fallen to you? Therefore, after your death, the throne should pass to your younger brother!"
The Grand Founder, kowtowing and weeping, replied, "I humbly accept your command."
The Empress Dowager turned to Zhao Pu and said, "My dear minister, remember these words for me as well—do not violate them!"
Zhao Pu repeatedly agreed and even wrote a sworn oath, which he stored in a gold-inlaid box, ordering a cautious palace attendant to keep it safe.
After hearing Zhao Pu's account, Emperor Taizong of Song began to understand: Empress Dowager Zhaoxian and Emperor Taizu had intended for him to pass the throne to Zhao Tingmei, who would then pass it to Zhao Dezhao—yet Tingmei seemed a bit too eager to claim it.
A few days later, Emperor Taizong of Song asked Zhao Pu whether he could pass the throne to Tingmei after his death. Zhao Pu replied, "The Grand Ancestor already made a mistake; how could Your Majesty make the same mistake again?"
Thus, Tingmei was exiled far away to Fangzhou, where he fell ill from melancholy and died.
Later, the idiom "One Mistake After Another" came to describe making a first error, failing to learn from it, making a second error, and repeatedly committing mistakes.
Source: *History of Song*, "Biography of Prince Tingmei of Wei"
Meaning of the Idiom: Later, the Chinese idiom "一误再误" came to describe how making a first error, failing to learn from it, making a second error, and repeatedly committing mistakes.