Happiness: Is There A Key?

"So, how exactly, do you decide to be happy?" My friend looked bemusedly at me as she replied to my statement that I thought happiness was a decision we made.
"LOOK at that tree!" I exclaimed loudly and with vehemence, knowing that my reply to her question required more than a little explanation.

My psychologist husband entered the fray by asking "Lin, when was one of your happiest times in your life?"
Silent for a moment, I thought about his question and reviewed major events in my life; hallmarks of 'happy' events asking myself if there were any times I could recall as being especially salient of happy times- graduations, becoming a Catholic, our marriage and then repeated what I'd said to our friend earlier but with different words. Happiness is a state of being achieved through will, like faith, like love.
One of the difficulties about happiness is that it's definitional. Happiness is unique to each of us because, by definition, each of is solitary, exclusive, an individual, with widely varying interests, skills, goals and desires: the desire for happiness is however, universal: We each want to be happy. We even wrote it into our Constitution: The 'unalienable right to the pursuit of happiness," Jefferson wrote, as if happiness were an object we must chase, hunt, inferring perhaps, an elusive goal.
The strong belief I have that happiness is a decision does not preclude any and all of the constant and realities of the varying emotional states that wander in and out of my psyche; rather happiness is a constant, a grounding, an undercurrent on which emotions appear and disappear, like the clouds in the sky. One of the obstacles to achieving a state of happiness is the belief that happiness is a feeling. A confusion which permeates two other decisions which are often confused with feelings for many of us: Love and Faith.
My non sequitur reply to my friend's question encompasses in four words what I consider to underlie the wisdom of happiness taught to me by a man earnestly in pursuit of a happiness which was eluding him, causing him to walk away from his ordination as a Catholic priest, to search for his own happiness by teaching young students like me what he was learning about happiness.
Frequently quoting Santayana's short poem or warning as it seemed to me back then,
Most people live their lives in the basement of a three story house
my teacher taught me and invaluable lesson about happiness at a time in my life of great, deep and painful unhappiness and it is this.
If you want to be happy, then act as if you are, take time to... LOOK at that tree!" Over time, the feeling will come, the knowledge that yes, I am happy... exactly like faith and love.
Although his admonition was metaphorical, there were many times during that phase of my life when nothing was clear and when I had no ground to walk on, no clue as to how I wanted to spend my life, only vague resolutions, that I would pull over to the side of the road and do exactly that. I would LOOK at that tree.