A tango is a dance that requires two people who should both get the tango done properly; even if one is out of step, the dance movements are not fluent. As an idiom it refers to a conflicting situation in which both the people involved are equally responsible for something, generally a fault.
1. The boss got annoyed when the two employees started blaming each other for messing up the records. He pointed out that both had been given the responsibility so it took two to tango.
2. The football authorities informed the coach and physical trainer that just as it took two to tango, both needed to work in tandem to get the team fit for the upcoming games.
3. The research mentor told the two students that if the project was to be successful, it required two to tango.