In order to uncover the processes that destroy unions, marital researchers study couples over the course of years, and even decades, and retrace the star-crossed steps of those who have split up back to their wedding day. What they are discovering is unsettling. None of the factors one would guess might predict a couple's durability actually does: not how in love a newlywed couple say they are; how much affection they exchange; how much they fight or what they fight about. In fact, couples who will endure and those who won't look remarkably similar in the early days. 

Yet when psychologists Cliff Notarius of Catholic University and Howard Markman of the University of Denver studied newlyweds over the first decade of marriage, they found a very subtle but telling difference at the beginning of the relationships. Among couples who would ultimately stay together, 5 out of every 100 comments made about each other were putdowns. Among couples who would later split, 10 of every 100 comments were insults. That gap magnified over the following decade, until couples heading downhill were flinging five times as many cruel and invalidating comments at each other as happy couples. "Hostile putdowns act as cancerous cells that, if unchecked, erode the relationship over time," says Notarius, who with Markman co-authored the new book We Can Work It Out. "In the end, relentless unremitting negativity takes control and the couple can't get through a week without major blowups."

U.S. News & World Report, February 21, 1994, p. 67.