One of them was about happiness and what to do to live a longer and happier life. It was one of the longest studies in human history, having been conducted for 75 years. It all started with teenagers filling out questionnaires about what they thought would make them happy. Most of them said what you would expect. Money, fame, successful careers, beautiful wives, family, good health, etc. They had to answer questions every year. Those who are still alive still do it today. Of course, there are many variables among the participants, but the one thing that resonated with everyone who reported living a happy life all these years was having great relationships with their spouse, family, and friends. Do you want to be happy until old age? Well… there you go. All You Need Are Healthy Relationships With Those Around You, Harvard's 75-Year-Old Experiment Says.