What's happiness means? How do you feel when you get to eat your favorite food item, or when you are going out with your friends to watch a movie of your favorite actor, or when you meet your best friend after a long time, or when you achieve something for which you were waiting from a long time. All these moments bring a beautiful smile at your face and that smile is not the fake one, it totally real and comes directly from your heart. Its like you were walking all alone in your thoughts might be day dreaming also, waiting for some miracle to happen and suddenly everyone and everything around you starts to work in the way that you have assumed it to be that it brings a huge smile to your face. That moment and that happiness can't be expressed in words, it can only be felt.
Some people have all the reasons to be happy but still their inner boundations doesn't allow them to enjoy that happiness. There are also who have no reason to smile but their strong will of being happy makes them to find millions of reasons to smile. When the sun sets, its not the end, but the beginning of a new story and a new morning. Its a psychological fact famously known as the "Law of Attraction" that if you will think positive and speak positive then it goes into the surroundings and bounces back to you and same applies with negative thoughts. So it depends on the person how he or she proceeds with his or her thought process because ultimately his vibes whether positive or negative bounces back to him.