Let me repeat it to you so you remember. The secret of happiness is to be happy. I'm not being intentionally flippant and I'm not trying to be overly arrogant. I'm not trying to overintellectualize happiness either. I really mean this.
Happiness is a state of mind.
You can be happy in almost any situation. Likewise, you can be unhappy in a equal number of situations. In the end, it's your decision. If one can control one's unhappiness, then one must be able to control one's happiness. As far as I know, the Human Genome Project has not been able to identify a single part of any human chromosome which is responsible for happiness.