“Everyone from the checkout clerk at Trader’s Joe to your great-aunt to Oscar-winning celebrities likes tell you that marriage is hard, but no one tells you how it is hard or what to do about it,” says Jo Piazza. It was that quandary—and her own first year of marriage—that compelled Piazza to ask hundreds of people from places as varied as Chile, Kenya, Denmark, India, and France about what exactly it takes to make a marriage work.