Dr. Tal Ben-Shahar taught the most popular course-Positive Psychology at Harvard University in 2006. Today I watched "Happiness 101 With Tal Ben-shahar" show on TPT and I can see why his lectures were popular. They are not only based on common sense, but also based on some scientific studies. Some of his ideas or tips on how to be happy such as: focus on what works, Learn to fail or fail to learn, deep breathing, give yourself permission to be human, express gratitude, exercises, simplify and more. Those ideas are common sense, he said what we need to do is to "make common sense more common". you can find some of his ideas including what is positive psychology from the following video.