司馬昭之心——路人皆知

From Cao Mao (Emperor of Cao Wei)'s statement of ousting Sima Zhao, before Cao was assassinated by Sima. This quote was later quoted by the historian Pei Songzhi in his annotated version of the Records of the Three Kingdoms:

景耀三年（魏景元元年），昭殺其主髦及王經。自曹芳事後，魏人省徹宿衛，無復鎧甲，諸門戎兵老弱而已。曹髦見威權日去，不勝其忿。乃召侍中王沈、尚書王經、常侍王業，謂曰：「司馬昭之心，路人所知也。吾不能坐受廢辱，今日當與卿自出討之。」 [MSC, trad.]

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景耀三年（魏景元元年），昭杀其主髦及王经。自曹芳事后，魏人省彻宿卫，无复铠甲，诸门戎兵老弱而已。曹髦见威权日去，不胜其忿。乃召侍中王沈、尚书王经、常侍王业，谓曰：「司马昭之心，路人所知也。吾不能坐受废辱，今日当与卿自出讨之。」 [MSC, simp.]

From: c. 3^rd Century, Xi Zuochi, The Annals of Han and Jin

Jǐngyào sān nián (wèi jǐngyuán yuánnián), zhāo shā qí zhǔ Máo jí Wáng Jīng. Zì cáofāng shìhòu, wèi rén xǐngchè sùwèi, wú fù kǎijiǎ, zhū mén róngbīng lǎoruò éryǐ. Cáo Máo jiàn wēiquán rì qù, bùshèng qí fèn. Nǎi zhào shìzhōng Wáng Chén, shàngshū Wáng Jīng, chángshì Wáng Yè, wèi yuē: “Sīmǎ Zhāo zhī xīn, lùrén suǒ zhī yě. wú bùnéng zuò shòu fèi rǔ, jīnrì dāng yǔ qīng zì chū tǎo zhī.” [Pinyin]

In Year 3 of Jingyao (Year 1 of Jingyuan of Wei, 260 AD), Sima Zhao assassinated the emperor Cao Mao and Wang Jing. (Before this,) Since the death of Cao Fang, the State of Wei has abolished the royal guards. There was no longer strong defense and only old and weak soldiers were left. Cao Mao felt that his authority was fading away and felt angry. Then he called Wang Chen, Wang Jing and Wang Ye, and told them, “Even people passing by know the ambition of Sima Zhao. I can't bear the humiliation of being dethroned. I think it's time to fight against him now.”