During the late Eastern Han Dynasty, a man named Zhang Fan came from a long line of officials but preferred a quiet life of study over wealth and status. When Grand Tutor Yuan Wei offered his daughter's hand in marriage, Zhang Fan politely declined. Despite repeated government summons to serve as an official, he never accepted.
Zhang Fan had a younger brother named Zhang Cheng, who was also widely known for his upright and honest character. The imperial court summoned him and appointed him as a Gentleman Consultant, and later promoted him to Commandant of Yique.
At that time, Dong Zhuo seized control of the court and wreaked havoc across the land
Zhang Cheng's younger brother Zhang Zhao, an imperial advisor, had just arrived from Chang'an and said to Zhang Cheng, "You want to kill Dong Zhuo, but you're outnumbered and outmatched. Your plan is too hasty, your strength far too weak—the chance of success is slim. In my view, Dong Zhuo is tyrannical and faithless; he won't last long. Better to choose a wise ruler to serve, wait for the right moment, and then act—that's what 'biding one's time' means, and only then can we fulfill our ambitions." Zhang Cheng agreed, resigned his official seal, took a back road home, and went into hiding with Zhang Fan in Yangzhou. The idiom "biding one's time" thus came to mean waiting for the opportune moment to take action.
Source: *Records of the Three Kingdoms*, Book of Wei, "Biography of Zhang Fan"
Meaning of the Idiom: Later, the Chinese idiom "待时而动" came to describe waiting for the opportune moment to take action.