Tā yuányǐn chényī-zhǔ'èr zhī shuō wèi zìjǐ de zhuǎntóu biànhù.
He invoked the old proverb 'one subject, two possible masters' to justify switching allegiance.
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history
An ancient proverb often cited in Warring-States and Three Kingdoms-era debates over loyalty. It was used by figures who left one lord for another - counter to the stricter Confucian ideal of 忠臣不事二主 ('a loyal minister does not serve two masters'). The two sayings represent rival ethical poles in classical Chinese political thought.