The enemy is right under our arm — we cannot fail to be vigilant.
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history
The set phrase 祸起肘腋 ('disaster rises from elbow and armpit') comes from 三国志·蜀书·法正传, describing how unrest can erupt from one's closest associates rather than distant enemies — a recurring theme in Chinese statecraft writing.
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Highly literary. In modern prose 肘腋 almost only appears in fixed expressions (祸起肘腋, 肘腋之患); never in casual speech.
