There have been several books written about the subject of happiness including several from Tal Ben-Shahar ("Happier", "Even Happier" and "Being Happy") and Zappos CEO, Tony Hsieh who wrote Delivering Happiness. All great books if you're looking for a deep dive into the subject of happiness. But I came across a quote from the Dalai Lama XIV that really nailed it for me:
Happiness is not something ready-made. It comes from your own actions.
Via The Learning Factor
Happiness comes from your own actions. Happiness is a choice. When you find yourself in an emotional state that you'd rather not be in, you have the power to change it in an instant.
happiness is matter of insight. no one can make you and sad without your permission.
The secret to happiness!