I think the ability to feel gratitude is a key to happiness. Some long time ago, I was afflicted with a major depression that limited the range of emotions I could feel pretty much to anger, fear, horniness, and loneliness. One thing I couldn't feel was gratitude. I was also extremely poor at the time.
One evening I was crossing a street on my way home, thinking about some potatoes and a little garlic I had at home for supper that night, when I noticed an unusual feeling. I couldn't identify it at first, but then it came to me that I was feeling grateful for the potatoes. I hadn't felt grateful for anything in at least a decade. Yet, almost the same moment I realized what I was feeling, I began feeling a bit cheerful. Not walking on air or anything like that, but just a wee bit cheerful. Ever since then, I've noticed that gratitude is quite frequently associated with cheer and happiness.
Perhaps because of my "dark" decades, I tend to feel gratitude these days for a whole lot of simple stuff -- a light breeze on a warm day, the sun dappling the grass in my yard, a moody, cozy fall day -- that sort of thing. But also a phone call from a friend or brother,
@YmirGF's insufferable humor, human beauty, the deep curiosity of the university student I'm tutoring, the folks who comment on my blog posts (they're wonderful!y upbeat and insightful!), and so forth.