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Phrase(s): make it one’s business to do something [and] take it upon oneself to do something
Fig. to do something on one’s own even if it means interfering in something that does not directly concern one. (As opposed to minding one’s own business.) • I know it doesn’t concern me, but I made it my business to call city hall because someone had to. • Jane took it upon herself to find out exactly what had happened to the old lady.
McGrawhill's American Idioms And Phrasal Verbs