I've heard, and do agree, that happiness can be summed up in one word: gratitude. There are people for whom happiness is a constant state of being. It's not temporal or conditional. A requisite for such a perspective is to be thankful for what one has. Of course, there are happy moments and unhappy moments--everyone has those. But it's how we view those "neutral" moments that really define whether we are happy individuals.
Sure, looking back at moments and recalling them as happy ones is nice, but how much better might they have been if we were able to appreciate them at the time? If we were able to stop complaining or moping enough to enjoy the scene and our company? I imagine the people around us would be happier for such a shift. For me, that's an element of happiness: spreading it to the people around me.
I have been so blessed with a life of good fortune. There are children all over the world who grow up in abject poverty and face some of the deepest atrocities of humanity. For the vast majority, the human experience is one of struggle, hardship and poverty. I've known nothing but love and comfort. Why was I so lucky? What did I do to deserve where I was born? The answer is: nothing. Therefore, I feel obligated to make sure that my good fortune was not given to me in vain and that I pass on the gifts and love I've been given to others.
Somehow, despite the lives they were born into, those "poor" children often smile more than those of us born in comfort and safety. It all comes back to gratitude. Do we realize how lucky we are to have food in front of us? Homes over our heads? No fear of bodily harm when we walk out our doors? Are we properly thankful for the family who cares for us? The friends who listen? We are so used to having these, we often forget how precious they are and how fortunate we are to have them. The less we forget... the more we appreciate... inevitably, the happier we'll be.
It doesn't need to be some complex or radical change of thought or the flipping of some magical switch. (And I assure you it is not found in weight loss or plastic surgery.) It need only be a reinforced sense of gratitude for the lives we live.
This is why happiness is not limited to moments fondly remembered, it can be a lifestyle choice.
Giving thanks before meals, before getting up in the morning, after another beautiful sunset... these are typically associated with religious rituals--which is perhaps why so many of us now reject them--yet they are simple and effective ways to systematically imbue each day with meaning and joy. My hope is that instead of happiness being something most of us only recognize in hindsight, it is something we feel in the present and are sure of as we look into the future.