冥思苦想

He puzzled his brains to find an answer.

他冥思苦寻求答案。

I puzzled over the problem for ages before the light suddenly dawned on me.

我这个问题冥思苦了很久才豁然。

As people grow older, they begin to ruminate on the uncertainty of life.

着年龄的增长，人们始生活的变化无常冥思苦。