Happiness is like a muscle, it must be exercised to stay healthy. Happiness is contagious - if you're near it, you'll catch it. Happiness has a direct relationship with good health. Time invested in working on happiness is an investment in your own future.
Happiness is natural to our species and absolutely essential to our health and well-being.
Yet, it is, by far, the most misunderstood human faculty. Modern society has reduced the idea of happiness to a bunch of simplistic cliches, used primarily to sell us stuff. It's important to know that happiness is much more than a good laugh or a fun day at the beach. Regardless of their current circumstances, any human on earth today can be happy. They have but to learn how to choose it.