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 …