Why would adding more negativity to an already hostile situation prove beneficial? Consider how parents typically react when they can’t get their children to stop quarreling: “I don’t care who started it—both of you, go to your rooms!” At first blush, a calmer, more soothing approach seems likely to be more effective. But as anyone with siblings knows, parents’ seemingly unsympathetic treatment of the situation can have an unusual effect. Siblings who moments before were threatening each other’s lives suddenly become more reasonable in contrast to their tyrannical parents, and even end up playing nicely after their banishment to their rooms. In difficult disputes, a similar recipe—adding a hostile third party to an interaction between two hostile parties—can improve people’s willingness to come to agreement, my research finds.

In our experiments, we created situations in which pairs of negotiators were part of a heated conflict. To get help resolving their issues, the negotiators could meet with a mediator. In some cases, the mediator had a “nice” approach—calm and polite. In others, he was hostile—aggressive and somewhat rude. Across different types of conflicts, we found that negotiators were more willing and able to reach an agreement with their counterpart in the presence of a hostile mediator than in the presence of a nice or neutral one.