Read more: We expect too much from our romantic partners

Poorer, less-educated Americans, especially those without a high-school degree, have exhibited the opposite trend. Although they are no less likely to cohabitate today than in previous eras, they are less likely to marry. When they do marry, they are less satisfied and more likely to divorce.

Social analysts have offered three major explanations for these marital difficulties. The first—that less-educated Americans have lost respect for the institution of marriage—is refuted by data. The psychologists Thomas Trail and Benjamin Karney conducted a definitive study asking Americans to indicate their agreement with the statement that “a happy, healthy marriage is one of the most important things in life.” The agreement rates were virtually identical among Americans of all income and education levels—and quite high all around.

The second explanation is that poorer, less-educated Americans have a different, perhaps faulty, vision of how an ideal marriage should work. Given the marital turmoil that started in the 1960s, it was reasonable to hypothesize that different segments of American society would arrive at different visions of the optimal marriage, and that some of these visions might be more conducive to happiness and longevity than others. But here, too, the best evidence suggests that most Americans, across income and education levels, have adopted a new marital ideal in which spouses look to each other not only for love, but also for self-expression and personal growth. Most Americans agree, for example, that “understanding each other’s hopes and dreams” is essential for a successful marriage—much more important than having sufficient savings, sharing values, or having good sex. Americans today want a partner who can help bring out their best self.

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The third explanation is that building and sustaining a marriage that meets these lofty aspirations typically requires substantial investments of time, attention, patience, and responsiveness, investments that are harder for poorer, less-educated Americans to make. When life happens—when the car breaks down or a ligament snaps—they are at greater risk for unemployment, eviction, and destitution. They tend to have less control over their schedules and less money to pay a babysitter, so they may struggle to get regular time alone with their spouse. When they find such time, they are more likely to arrive to the conversation feeling emotionally depleted from other stressors, and the topics of discussion—how to stretch the money this month, how to wrangle child care with a demanding work schedule—are often thornier. The evidence is generally supportive of this third explanation: a major reason why the marriages of poorer, less-educated Americans are struggling is that economic realities make it difficult to live up to the new cultural ideal. This struggle is leading many to opt out of marriage altogether and, for those who opt in, to make the path to marital success more challenging.