Idiom: "(to) knock oneself out"
Definition:
to work very hard at something (sometimes too hard)
Examples:
1) Larry knocked himself out trying to study for his GREs.
2) Don’t knock yourself out trying to help Sam. He won’t appreciate it anyway.
中文解释：http://www.youzienglish.com/main/idiom_of_the_day/to_knock_oneself_out/cn/
