Public officials must not harm the public interest for their own private gain.
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history
From 李格非's 《书洛阳名园记后》 (Northern Song): rulers who 放乎一己之私 - let private interest run wild - and forget the empire's order will lose their position. The phrase carries this old moral weight.
register
Formal and judgmental - used in editorials, court decisions, moral arguments. Rare in casual speech. Almost always negative; a near-synonym for 私心 (sīxīn) but heavier.