先下手為強

First attested in 1162–1163, in The Account of the Battle of Caishi and the Demise of Wanyan Liang (《采石瓜洲斃亮記》):

諸酋退曰：「南軍有備，豈宜輕舉？輕即送死。今亮以險狠拒諫，吾等有言不從，必殺我，不如先下手為強也。」遂定謀殺亮。 [Written Vernacular Chinese, trad.]

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诸酋退曰：「南军有备，岂宜轻举？轻即送死。今亮以险狠拒谏，吾等有言不从，必杀我，不如先下手为强也。」遂定谋杀亮。 [Written Vernacular Chinese, simp.]

Zhū qiú tuì yuē: “Nán jūn yǒu bèi, qǐ yí qīngjǔ? Qīng jí sòngsǐ. Jīn Liàng yǐ xiǎnhěn jùjiàn, wúděng yǒu yán bùcóng, bì shā wǒ, bùrú xiān xiàshǒu wéi qiáng yě.” Suì dìng móushā Liàng. [Pinyin]

The chieftains withdrew and discussed among themselves: “The southern army is well-prepared. How can we launch a rash action? To act rashly would be to march to our doom. Now, Wanyan Liang, in his recklessness and treachery, rejects all counsel. Rather than risk speaking up and being killed for it, it is better to strike first.” Thus, they resolved to assassinate him.

先下手為強

1. to strike first and gain the upper hand