家贼难防: a thief in the family is difficult to detect.; a thief from within is hard to guard against.; it's most difficult to forestall a thief within the house
野贼好捉家贼难防: it's easier to guard against an external enemy than an internal enemy
Example Sentences:
1.
Flaw essential self - protection - losing in the internal section or thief within family 缺失必要自我保护输在内部小节家贼
