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 the science of happiness for over 20 years from a logical and philosophical prospective, using flow charts and formulas to get to the root of unhappiness. A while back, he learned a habit that can almost instantly help you find joy and fulfillment.