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Jyutping zi1 jan4 hau2 min2 bat1 zi1 sam1
Pinyin zhī rén kǒu miàn bù zhī xīn

Definitions (Wiktionary)
  1. proverb, Cantonese
    one may know a person from the outside but may not understanding their true nature
    (syn.) 知人知面不知心

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Jyutping zi1 jan4 hau2 min6 bat1 zi1 sam1
Pinyin zhī rén kǒu miàn bù zhī xīn

Definitions (CC-CANTO)
  1. (proverb) people cannot understand others from the person's appearance
Definitions (粵典–words.hk)
  1. 語句
    從​人​嘅​外表​唔​能夠​知道​佢​嘅​內​心​係​點​,​辨別​唔​到​佢​係​好人​定壞​人
    people cannot understand others from the person's appearance
    • 知人口面不知心,呢個世界唔係咁簡單㗎。
      知人口面不知心,呢个世界唔系咁简单㗎。
      zi1 jan4 hau2 min6 bat1 zi1 sam1, ni1 go3 sai3 gaai3 m4 hai6 gam3 gaan2 daan1 gaa3.
      You can't know people's mind from their faces. The world is not that simple.
Examples (粵典–words.hk)
  1. Cantonese
    知人口面不知心,呢个世界唔系咁简单㗎。
    知人口面不知心,呢個世界唔係咁簡單㗎。
    zi1 jan4 hau2 min6 bat1 zi1 sam1, ni1 go3 sai3 gaai3 m4 hai6 gam3 gaan2 daan1 gaa3.
    • You can't know people's mind from their faces. The world is not that simple.
  2. Cantonese
    知人口面不知心
    知人口面不知心
    zi1 jan4 hau2 min6 bat1 zi1 sam1
    • You can't know what someone is thinking in his head.