In 688 BCE, King Wen of Chu launched a campaign against the state of Shen. As his army passed through the state of Deng, the ruler, Marquis Dengbu, warmly hosted his nephew, King Wen, with a grand banquet and invited him to stay for several days.
Deng Buhou had three nephews named Zhui, Dan, and Yang. Seeing that King Wen of Chu harbored ambitions and ill intentions toward the state of Deng, they urged their uncle, "Take advantage of his trust and kill him now to eliminate the threat." When Deng Buhou refused, they pressed, "The one who will destroy Deng is none other than King Wen of Chu. If you don't strike now, you'll be like a man trying to bite his own navel—utterly helpless and full of regret. The time to act is now."
But Deng Buhou still refused, saying, "If I kill King Wen of Chu, others will think I would even kill my own nephew, and no one would come to visit me." The three nephews urged him again, "If Your Majesty does not listen to us, the state will perish. When that happens, what guests will you entertain?"
Deng Buhou still refused to listen.
Some days later, King Wen of Chu led his army to conquer the state of Shen. On the return march, he launched an attack on the state of Deng, but Deng's forces were still strong at the time, and he failed to destroy it.
Ten years later, King Wen of Chu launched another campaign against the state of Deng, and this time Deng was ultimately conquered and annexed by Chu.
Later, the idiom "Too Late to Bite One's Navel" came to describe situations where things cannot be undone and regret is futile.
Source: *Zuo Zhuan*, Chapter "Duke Zhuang's Sixth Year"
Meaning of the Idiom: Later, the Chinese idiom "噬脐何及" came to describe how things cannot be undone and regret is futile.