Being happy is different for each person obviously, but I think the "expectations" part of the article's equation is the most important. When I look at certain parts of my life - work, social (including family and friends), and general wellbeing, I think I can safely say I am happy, but I have also tempered my expectations to account for this.
My job is challenging, but I am still happy with being a lawyer at my firm. Sure, some days I actually walk into work with the explicit thought of "this day is going to suck", but as long as I know that going in, then it will all be fine. Usually those are the days when I'm trying to close a deal and know I'll be dealing with difficult clients or lawyers, or when I know I'm not going to have enough time to get stuff done.
Of course I argue with my husband and yell at E a little too often, but this is obviously a part of being married and raising a small child.
I don't tend to worry about things that I cannot change, even if I am disappointed by them. Of course, the revers of doing that means that you don't expect more when you do deserve it or when you could do better. It is a balancing act, and happiness is on a spectrum. I certainly don't feel completely happy each and every moment of the day, but generally I feel pretty good about my life and the people in it.
Things that contribute to my happiness - getting stuff done, being organized, looking after my family's needs, having people over to visit, being challenged at work and finding the answers, sharing jokes with friends, having something to look forward to (like a holiday or trip), and seeing E enjoying life.
A rolling stone gathers no moss, so I didn't lie in the grass for too long that day;)