During the Spring and Autumn Period, Prince Chong'er of Jin, persecuted by his stepmother, was forced into exile for 19 years. Eventually, with the help of Duke Mu of Qin, he returned to become ruler, known historically as Duke Wen of Jin.
After Duke Wen of Jin took the throne, he devoted himself to governance and revitalization, and the state of Jin quickly grew powerful.
Among the feudal states of the time, the Kingdom of Chu was immensely powerful, dominating several smaller neighboring states and acting as the undisputed hegemon of the Central Plains.
In 632 BCE, Duke Wen of Jin decided to challenge the hegemony of Chu, personally leading his army to attack the small states of Cao and Wei, which were allied with Chu.
At the time, King Cheng of Chu sent his general Ziyu to lead reinforcements. Shortly after Ziyu's departure, the king grew uneasy and wrote to him, warning, "Duke Wen of Jin spent nineteen years in exile before returning to rule. He has endured every hardship and knows the people's hearts well. He is experienced in governance, leadership, and warfare. You face a formidable enemy—do not take him lightly, or you will suffer greatly."
When Ziyu received King Cheng of Chu's letter, he dismissed its warnings with a scoff
Later, the idiom "difficulties and dangers" came to describe many hardships, perils, and obstacles on the path forward.
Source: *Zuo Zhuan*, Chapter "Duke Xi's 28th Year"
Meaning of the Idiom: Later, the Chinese idiom "艰难险阻" came to describe many hardships, perils, and obstacles on the path forward.