Basically, the couples who had shown the most activity on the physiological testing—more rapid heart rate, more active sweating, faster blood flow—were the ones whose relationships were more likely to have collapsed. Their high states of arousal indicated they were in fight-or-flight mode, prepared to attack their partner or prepared to be attacked. Their relationships were based on hostility and criticism.
The couples who had stayed together, however, had shown less dramatic changes on the tests, even when they fought. They had displayed kindness and generosity.
Gottman then conducted another experiment involving 130 newlyweds. The couples were observed during a weekend retreat as they went about their normal daily tasks, and that’s when the psychologist uncovered the secret to why some relationships flourish and others fail.