大智若愚 -------Still waters run deep

例句：

A: He's a man of few words. I doubt if he's somewhat slow in reaction.
他很少说话，我怀疑他是否有一点反应迟钝。

B: Oh, no. He's quite clever. Do yon know still waters run deep?
噢，不。他相当聪明。你可知道大智若愚吗？

同义词：
He's not a wise man who cannot play the fool on occasion.