"When you're in a healthy relationship," said Rachel Sussman, "it can throw a little sunshine on everything in your life."
Even when you've had a harrowing day at work, or an argument with a friend, you know you'll come home and get to hang with the person who makes you the happiest.
"You feel hopeful," said Sussman, who is a couples therapist. You're watching each other's backs, and "that can give you a real feeling of comfort and security."
So when Sussman tries to discern a couple's status — in terms of whether they're heading for divorce — she looks for one sign in particular: hopelessness.
"You just feel that there's nothing else that can be done to save the relationship," Sussman told Business Insider of her clients who are on the verge of a breakup. "You are coming to terms with the fact that it's ending, and that can make you feel hopeless about the relationship, but also hopeless about your life."
Indeed, a 1992 study by researchers at the University of Washington found that marital disappointment and disillusionment — which encompasses feelings of depression and hopelessness — "was the most powerful single predictor of divorce." Specifically, couples who felt hopeless at the study's outset were more likely to be divorced three years later.
The researchers write that, among the couples they interviewed who showed signs of disappointment and disillusionment, some said they'd had unrealistic expectations about what marriage would be like.
Read more: 8 things science says predict divorce
From marriage and family therapist Hal Runkel's perspective, a relationship's prognosis comes down to the couple's willingness to invest effort into it. "When one spouse is indifferent," as opposed to enraged, he wrote in an email to Business Insider, "they no longer care that much about how their spouse feels and behaves."
He added, "They don't care that much about staying in a relationship at all, much less doing whatever it takes to make it work."
