Researchers wondered how can a couple part ways after 40 years of living together even as the shocking news of Former US Vice President Al Gore's divorce with wife Tipper hit headlines.
Even Robert Levenson, a psychologist at the University of California, Berkeley, delved deeper into couples' psyche to know the answer.
"It's striking when a couple has been together 40 years and then they call it quits. It's not what we would expect," Live Science quoted Levenson as saying.
Marriages get in trouble when the couple's situation or relationship changes and the partners cannot adapt, Levenson said.
A 2000 study published in the Journal of Marriage and the Family by Levenson and psychologist John Gottman, now at the Gottman Relationship Institute, found that divorces during this period are tended to be marked by anger and vicious fights and also by coldness and emotional withdrawal.
The researchers cited "growing apart" as a common reason for midlife divorces.
Relationship ruts and boredom are common. Spouses forget to show appreciation for each other, leading to frustration and loneliness.
Terri Orbuch, a University of Michigan psychologist and author of "5 Simple Steps to Take Your Marriage from Good to Great" research has shown that marriages with husbands who don't feel appreciated are twice as likely to end.
"Things can start out small and seemingly insignificant," Orbuch said.
"What happens is they accumulate over time and they become bigger and bigger," he added.