make it business to

make it (one's) business to (do something)

To decide to do something in which one was not involved or that was not one's responsibility. I know you think you shouldn't get involved, but this is serious enough that you need to make it your business to intervene.
See also: business, make

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.
See also: business, make