For 86 years, researchers at Harvard have been studying the lives of hundreds of people and their families to discover what makes us happy.

For example, the Harvard Study of Adult Development found that happy people tend to have good conflict-resolution skills, exercise often and maintain positive relationships.

Dr. Robert Waldinger, the study's director and a professor of psychiatry at Harvard Medical School, recently appeared on Simon Sinek's "A Bit of Optimism" podcast.