箭在弦上 Arrow on the string
Explanation
比喻事情发展到不得不采取行动的地步。
It means that things have reached a point where one has no choice but to act.
Origin Story
东汉末年，群雄逐鹿，曹操势力日益壮大。袁绍为对抗曹操，召集谋士陈琳，命其撰写檄文，讨伐曹操。陈琳挥毫泼墨，写就一篇气势磅礴的《讨曹檄文》，痛斥曹操罪行，字字诛心。檄文一出，天下震动，袁绍大军士气大振。然而，官渡之战，袁绍惨败，陈琳也随之投降曹操。曹操问及此事，陈琳坦言，当时形势所迫，箭在弦上，不得不发。
At the end of the Eastern Han Dynasty, numerous warlords were vying for dominance. Cao Cao's power grew increasingly strong. Yuan Shao, to counter Cao Cao, summoned the strategist Chen Lin and ordered him to write a manifesto to denounce Cao Cao. Chen Lin, with full effort, penned a powerful manifesto condemning Cao Cao's crimes. The manifesto caused a sensation throughout the land. Yuan Shao's army was greatly encouraged. However, at the Battle of Guandu, Yuan Shao suffered a devastating defeat, and Chen Lin subsequently surrendered to Cao Cao. When Cao Cao questioned him about this matter, Chen Lin honestly stated that he was then under immense pressure. The arrow was on the string, he had no choice but to act.
Usage
形容形势紧迫，不得不采取行动。
It is used to describe the urgency of a situation and the necessity to act.
Examples
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战事一触即发，箭在弦上，不得不发！
zhanshi yichu ji fa, jian zai xian shang, budebu fa!
The war was imminent, the arrow was on the string, and there was no choice but to fire!
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他已箭在弦上，必须做出决定。
ta yi jian zai xian shang, bixu zuochu jueding
He was under pressure and had to make a decision; the arrow was on the string.