it takes two (to do something)

Two parties are responsible for a certain action or situation in which they are involved. Your son is blaming mine for what happened, but it takes two to get into a fight. We're all ready for the merger, but it takes two to make a deal this big work, and the other company has been dragging its heels on the paperwork. No, I don't fully believe either of them. I know it takes two to quarrel!

it takes ˈtwo (to do something)

(also it takes two to ˈtango) (saying) used to say that something cannot be the fault or responsibility of one person alone: You’ve only heard his side of the story. It takes two to have an argument, you know. ♢ The company is ready to sign the agreement now, but it takes two to tango and the negotiations may continue for several days yet.