Gottman is a world-renowned relationship expert, and his work has changed the way we think about love and marriage. His research includes studying what he calls "the masters and disasters of love"—couples who have either made their relationship work or seen it fall apart. After studying these couples, Gottman was able to identify four behaviors that he called "the four horsemen of the apocalypse." These four behaviors—criticism, contempt, defensiveness, and stonewalling—were present in every failed relationship, while couples who had lasting relationships did not exhibit these behaviors.

Criticism is when you attack your partner's character rather than their behavior. For example, "you're such a slob" is a criticism, whereas "I don't like it when you leave your clothes on the floor" is not.

Contempt is when you see your partner as beneath you and speak to them accordingly. This could manifest as name-calling, eye-rolling, or mockery.

Defensiveness is feeling the need to justify your actions instead of taking responsibility for them.

Stonewalling is shutting down emotionally and withdrawing from the conversation altogether.