In the country of the blind the one-eyed man is king. 
比上不足，比下有餘。

A friend in need is a friend indeed. 
患難見真情。

A leopard cannot change his spots. 
本性難移。

A little learning is a dangerous thing. 
只知皮毛是件危險的事。

A rolling stone gathers no moss. 
滾石不生苔；轉業不聚財。