Harvard started looking into what makes people happy in 1938 with its Harvard Study of Adult Development. The most important finding of this study is that health flows from how happy people are with their relationships. If people are isolated or suffer from conflict-ridden relationships, their health and happiness deteriorate. If people have good relationships with family, friends, and the community, they live longer, they're healthier, and they're happier.
The study found that living in conflict is bad for people's physical and emotional health. Fixing or ending toxic relationships is the most time-sensitive problem in a person's life. Health and happiness can improve most quickly by making a change in any relationship that leaves you feeling tired of fighting at the end of each day.