大智若愚
No man can play the fool so well as the wise man.
He is not a wise man who cannot play the fool on occasion.

eg：Silent man, like still waters run deep and dangerous.

中英俚语俗语来源：老子：“大智若愚。”

同义词：深藏不露 To humble oneself.
反义词：不懂装懂 Assume a knowing air.