Sex makes babies. So it is ironic that the child, the embodiment of the couple's love, so often threatens the very romance that brought that child into being. Sex, which set the entire enterprise in motion, is often abandoned once children enter the picture. Why does parenthood so often deliver such a fatal blow?

Throughout the 1980s and 1990s, in a specially outfitted studio apartment in Seattle that reporters nicknamed the "love lab," mathematician-turned-psychologist John Gottman videotaped ordinary couples in their most ordinary moments. Sometimes Gottman asked them to discuss an area of conflict while monitors strapped to their chests recorded their heart rates. Sometimes he sat them on spring-loaded platforms to record how much they fidgeted. He looked at how they brought up painful subjects, how they responded to each other's bids for attention, how they fought and joked, and how they expressed emotion.

As a graduate student, I'd done individual counseling before, and had worked with parents and kids, but had never worked with a couple. Thirty minutes into the first session, when I was lost in the midst of a meandering series of questions, the husband leaned forward and said, "I don't think you know what you are doing." Alas, he was right. Naked came the new couples therapist.

Many therapists define the type of therapy they practice by taking a head count: if one person is present, they're practicing individual therapy; if two or more people are present, it's couples or family therapy. I believe this is misguided the key to determining which brand of therapy is in use at any given point lies in the therapist's orientation and focus, not the number of people occupying space in the room.