When Daniel Cox, a researcher at the American Enterprise Institute, looks at the state of marriage today, one thing stands out: A successful and enduring marriage isn’t just about what a married couple does, but also what the people around them do and say.

“Our social environment — the people we hang around — profoundly influences our behavior," Cox wrote in a recent edition of “ American Storylines .” Just as people are more likely to take up smoking cigarettes if they hang out with people who smoke, “Research has shown that if a friend gets divorced, your odds of also getting divorced increase dramatically.”

That has led to the idea that divorce can be contagious , and there’s research that confirms this idea. Most recently, polling by the Survey Center on American Life earlier thi

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