John Gottman has changed the way many people look at relationships. While anecdotal stories can be interesting, he is a scientist. He collected evidence that is not subject to the whim of the observer.

In the Love Lab he hooked couples up to wires that measured all manner of physiological symptoms of stress. If you are angry, your plastered grin and masked words might hide it but your heart rate can't. Couples who are choleric when they interact, as measured by heart rate and sweat, are headed for a split. 

The clincher he claims is what he calls turning towards your partner. If a wife sees a bird and makes a "bid" for attention, her husband has a chance to turn toward her or away. 

"Bob, do you see at that bird? Isn't it gorgeous?"

"Uh huh," he grunts without looking up from his phone. Gottman would score that as a non response. Healthy couples, those he named Masters, catch those bids for attention 87% of the time. They are still happily married six years later. The group that only responds a third of the time, those he coined Disasters, aren't. 

The article a friend sent me sums it up in two words. Kindness and generosity.

Like the two wings of a bird.