Happiness is something which comes out from inside, mostly it doesn't depend upon the outward condition, such as what you have or what you lack. But it depends upon how you react to any circumstances. Let's suppose two students given exam of 12th grade and both achieved similar numbers, one has the habit of looking positive sides of the things, so he shown his happiness as he get this much numbers, if he wouldn't get this then what he would have to do. While other started crying as he just got this numbers he was deserving more.
The point is, if we want to be happy then we need to think over the positive sides of things. We need to struggle for the best but after getting the result, we need to learn how to accept it willingly. It is for our own health, our own physical and mental fitness.