一家唔知一家事 [－－－－－－－]

Jyutping jat1 gaa1 m4 zi1 jat1 gaa1 si6
Pinyin yī jiā wú zhī yī jiā shì

Definitions (粵典–words.hk)
  1. 語句
    形容​外人​唔​會​知人​地​嘅​隱​情​同​苦衷
    outsiders have no idea what happened behind; literally: a family does not know another family's affairs
  2. 近義詞
    家家有本難念的經
Definitions (Wiktionary)
  1. phrase, Cantonese, idiomatic
    Outsiders have no idea what happens within a family