I’ve long ben familiar with John Gottman’s research on marital relationships. This Business Insider article sums up some of his main findings of what it is that makes a relationship work over the long term. Here’s an excerpt:

In the 2006 study, Gable and her colleagues followed up with the couples two months later to see if they were still together. The psychologists found that the only difference between the couples who were together and those who broke up was active constructive responding. Those who showed genuine interest in their partner’s joys were more likely to be together. In an earlier study, Gable found that active constructive responding was also associated with higher relationship quality and more intimacy between partners.

There are many reasons why relationships fail, but if you look at what drives the deterioration of many relationships, it’s often a breakdown of kindness. As the normal stresses of a life together pile up—with children, career, friend, in-laws, and other distractions crowding out the time for romance and intimacy—couples may put less effort into their relationship and let the petty grievances they hold against one another tear them apart.