司馬昭之心——路人皆知

From Cao Mao (fifth emperor of Cao Wei)'s statement of ousting Sima Zhao the night before getting assassinated by a servant of Sima on June 2, 260 C.E.. This text was later quoted by the historian Pei Songzhi in his annotated version of the Records of the Three Kingdoms:

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。」 [Classical Chinese, trad.]

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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。」 [Classical Chinese, simp.]

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

Zì Cáo Fāng shì hòu, Wèi rén shěngchè sùwèi, wú fù kǎijiǎ, zhū mén róngbīng lǎoruò éryǐ. CáoMáo jiàn wēiquán rì qù, bùshēng qí fèn. Nǎi zhào shìzhōng Wáng Shěn, 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]

Since the dethronement of Cao Fang, royal guards had been abolished in the State of Wei. Strong defense no longer existed; only old and weak soldiers remained. Raging against his authority fading away, Cao Mao called Wang Chen, Wang Jing and Wang Ye and told them, “Even passers-by know the ambition of Sima Zhao. I can't bear the humiliation of being dethroned anymore. I think it's high time for us to bring him down now.”

司馬昭之心——路人皆知

1. one's evil ambitions are apparent to everyone