Everyone has something different that makes them happy. Trick is to find it and enjoy it. If you spend your time complaining about everything, you'll probably never know it when you do find it.
Have a great holiday, if you're in an area that celebrates.
What is there to understand? Happiness is being joyful about the way things are in your life, but there will always be periods of sadness to remind you how precious a gift happiness is. Therefore, try to see the good in everything.