work hard play hard的意思是努力工作努力玩。hard主要用作为形容词、副词、名词，作形容词时意为“努力的；硬的；困难的；辛苦的；确实的；严厉的；猛烈的；冷酷无情的”，作副词时意为“努力地；困难地；辛苦地；接近地；猛烈地；牢固地”，作名词时意为人名。

例句：

Why do they have to work so hard?

他们为什么工作必须那么努力。

Every one of us should work hard for the prosperity of our country.

我们每一个人都应该为我们国家的繁荣而努力工作。

I find it hard to trust not only me, but everyone around me, Because of.

因为你，我发现很难再相信我自己以及周围的每一个人。

The ground is as hard as stone after the long drought.

长期干旱之后，土地硬得就像石头一样。

It's very hard to maintain a relationship.

要维持一段关系，是很困难的。

It's very hard on parents when their children are rebellious.

对父母来说，孩子叛逆是个很棘手的问题。