“It isn’t what you have, or who you are, or where you are, or what you are doing that makes you happy or unhappy. It is what you think about.” ~ Dale Carnegie
And that right there is why I say happiness is a choice. 
It is a choice because once you know what makes you unhappy, you'll not want to stick around and wait for it to bring you unhappiness, will you? A normal person will not. He or she will gravitate towards what brings them happiness. 
Alot may not be going the way you want it to, but that's not a ticket for you to be unhappy. Instead, choose what you allow your thoughts to dwell on but don't encourage negative thoughts in your mind.

"There is only one way to happiness and that is to cease worrying about things which are beyond the power of our will.” ~ Epictetus

Choose to be happy even when you feel you shouldn't, and happiness will follow you wherever you go. 
 

Ignite happiness wherever you are. Inspire and influence others with your thoughts and words, causing happiness. 
Just be a highly flammable ball of Happiness