Many people expect marriage to bring constant happiness, but leading American psychologists say that is an unrealistic expectation. Drawing on research by Dr. John Gottman and insights from Harvard-trained psychiatrist Dr. Kavetha Sun, experts explain why healthy marriages are built on repair, communication and mutual respect rather than perfection. They also highlight four toxic habits—including criticism, defensiveness, contempt and avoiding difficult conversations, that can slowly damage a relationship if left unchecked.