知其一,不知其二 [－－－－－－－－]

Jyutping zi1 kei4 jat1 , bat1 zi1 kei4 ji6
Pinyin zhī qí yī , bù zhī qí èr

Definitions (CC-CANTO)
  1. (slang) someone knows one-side of a story, s/he only knows half of the truth