What helps a marriage thrive? John Gottman, one of the world's leading researchers on marital relationships, looks for the presence of contempt or kindness within the marriage. Here's what the research has found:

Contempt is the number one factor that tears couples apart. People who are focused on criticizing their partners miss a whopping 50 percent of positive things their partners are doing and they see negativity when it's not there. People who give their partner the cold shoulder—deliberately ignoring the partner or responding minimally—damage the relationship by making their partner feel worthless and invisible, as if they're not there, not valued. And people who treat their partners with contempt and criticize them not only kill the love in the relationship, but they also kill their partner's ability to fight off viruses and cancers. Being mean is the death knell of relationships.

Kindness, on the other hand, glues couples together. Research independent from theirs has shown that kindness is [one of] the most important predictors of satisfaction and stability in a marriage. Kindness makes each partner feel cared for, understood, and validated—feel loved. A line from Shakespeare captures the spirit of kindness: "The more I give to thee, / The more I have, for both are infinite." That's how kindness works too: there's a great deal of evidence showing the more someone receives or witnesses kindness, the more they will be kind themselves, which leads to upward spirals of love and generosity in a relationship.