تعریف و معنای "for the life of {sb}"

What is the origin of the idiom "for the life of someone" and when to use it?

The origin of the idiom "for the life of someone" is unclear, but it has been used since at least the early 19th century. It likely evolved from earlier expressions in English that emphasized the importance or difficulty of preserving someone's life. This expression is used to express a sense of frustration, puzzlement, or inability to accomplish a task or recall information, especially when trying very hard.