Yale's Most Popular Course in History Teaches You to Be Happy—and It's Available Online. Psychology 157 (free online) [coursera.org] So what do you think you would change that would make you more happy?
When I first read your headline, being a the literalist that I am, took it to mean that Yale has a very popular History course (as in, Course in History)! How disappointed I was to learn that the course came from the Behavior Sciences department!