be brother's keeper

be one's brother's keeper

to be responsible for someone else. (Used of others besides just real brothers.) I can't force these kids to go to school and get an education so they can get jobs. I am not my brother's keeper. You can't expect me to be my brother's keeper. Each of us should be responsible for himself! be one's own man and be one's own master to be someone who is not controlled by other people; to be an independent person. Bert longed to be his own master, but at the same time feared losing the security he had as the employee of a large company. When I go away to college, I'll be my own man. My parents won't be able to tell me what to do anymore.
See also: keeper

not be your brother's keeper

  also not be somebody's keeper
to not be responsible for what someone does or for what happens to them It's all too easy for us not to intervene in another country's problems, telling ourselves that we're not our brother's keeper. You shouldn't blame yourself for what's happened to Simon. You're not his keeper, you know.
See also: keeper