I firmly believe that the most enduring of marriages are made of people who are, not the best matched, but who are the most committed fighters. Marriage isn't about finding the perfectly compatible person, even though compatibility has a helpful place. It's much more about finding a good person to fight for who will fight for you, too. That fighting? That bloody-nosed refusal to lay down and quit? That's what commitment looks like. Commitment, real and long term, takes a rough strength. Pledging vows is easy in the heat of infatuation; "In sickness and in health" is an easy promise in the midst of health and youth. It is a harder vow to hold when it is ugly and overweight, tired and sick and irritated. It's harder to hold to when it is aging and angry, insecure and emotional. It's hard to stay when you want to leave. It's hard to still commit when it's no longer easy. But, in a marriage, we promised to commit then, too: in weak...