冥思苦想

He puzzled his brains to find an answer.

他思苦想寻求答案。

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

我这个问题思苦想了很久才豁然开朗。

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

随着年长，人们开始生活变化思苦想。