It takes two to tango

Both people/groups involved in something must take responsibility

e.g. my sister apologised for continuing a feud between us but to help mend our relationship I reminded her that it takes two to tango.

- There was a song if that name in the 1950s which made the phrase popular:
https://www.youtube.com/watch?v=95BeBGTF7-M
https://www.youtube.com/watch?v=H4iMNrwGBbQ