Happiness researcher shares his '90-second rule' to live a better, more fulfilled life—it helps when you're angry or upset

Mo Gawdat's son, Ali, was 21 years old when he died due to medical negligence during a routine appendix surgery in 2014. Gawdat was devastated, confused and in a palpable state of shock. Then, 17 days later, he started writing a book on how to be happy, in his son's honor. Gawdat has researched…