The symptom theory has several problems. First, it reinforces the idea that there is such a thing as a perfect marriage that will inoculate us against wanderlust. But our new marital ideal has not curbed the number of men and women who wander. In fact, in a cruel twist of fate, it is precisely the expectation of domestic bliss that may set us up for infidelity. Once, we strayed because marriage was not supposed to deliver love and passion. Today, we stray because marriage fails to deliver the love and passion it promised. It’s not our desires that are different today, but the fact that we feel entitled—even obligated—to pursue them.

Second, infidelity does not always correlate neatly with marital dysfunction. Yes, in plenty of cases an affair compensates for a lack or sets up an exit. Insecure attachment, conflict avoidance, prolonged lack of sex, loneliness, or just years of rehashing the same old arguments—many adulterers are motivated by domestic discord. And then there are the repeat offenders, the narcissists who cheat with impunity simply because they can.