Hǎo lǎoshī bùbì bóxué, zuò de chéng yīzìshī jiù gòu le.
A good teacher doesn't need vast learning - being a one-character mentor is enough.
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history
Two sources: a humble clerk correcting 李相's mispronunciation of a 《春秋》 character (《唐摭言》), and the poet 齐己 changing 数枝开 to 一枝开 on 郑谷's suggestion - the single edit turned a 'plum in bloom' into an 'early plum.' 郑谷 was thereafter called 一字师.
