Why humans cannot be completely happy

What do humans want? To be happy. But what is happiness? Happiness, apparently, is that thing which humans really want. Ahem. With a circular definition, it would be no wonder that people find happiness elusive. The definition I found in Aristotle's Nichomachean Ethics was along the lines of "the final human good, the end to which other goods are merely means", which isn't much more helpful. Off-topic, Aristotle's ideas have tremendous staying power in terms of influencing Western thought through to the present - despite whoppers like the idea that heavy objects fall faster than light ones (on the basis that the rightful place of all objects was at the centre of the universe, and heavy ones have a greater will do it), and the "men are rational while women are emotional" line from Politics that has supported millenia of sexist social structures. It took Galileo, Kepler and Newton to untangle the former, and even the most "developed" societies haven't completely gotten over the latter. On the other hand, the Ethics wasn't intended to be a philosophical treatise - it's really his lecture notes for the very first secular 'practical guide to living' course directed to the men of the Greek upper classes - two thousand-odd years before Dale Carnegie and the self-help fads. Being more practical than most philosophers since Aristotle, psychologists helpfully use "subjective well-being" in place of "happiness". Interestingly, in Aristotle's Nichomachean Ethics, the word translated as "happiness" is "eudaimonia", which literally means "living under a good spirit". Subjective well-being seems a better translation in general - although it wouldn't be fully consistent with the uses of the word in the Ethics. Subjective well-being tells us just what it is: a state of mind. Empirical research bears this out: if you are asked about finances just before being asked "All things considered, how satisfied are you with your life as a whole these days?", then priming effects makes finances weigh heavily on the judgement of overall happiness. The same thing happens when primed with questions about one's love life, or physical health. Hundreds of factors make up subjective well-being. To name a few from my own brainstorming (more ideas welcome):

• Physical: health, exercise, nutrition, sleep, appearance
• Personal: adventure, change, direction and goals, financial stability, personal development, relaxation, work, peace (vs anxiety)
• Interpersonal: social activity and acceptance, peace (vs conflict), altruism, friendship, intimacy (love life), community, family
• Intellectual: aesthetic appreciation, creative expression, intellectual exploration and engagement

The exercise leads me to draw three conclusions: (1) human brains can't weigh up so many factors at once, so subjective well-being gets thumbsucked from whatever seems salient at the moment (easily influenced by priming), and (2) with so many factors, at least a few will be going wrong at any point in life. Subjective well being will therefore always have room for improvement - unlike the "now I can die happy" cliche of attaining perfect happiness. And (3) the whole thing is subjective: which factors count the most, and how much detail each one goes into (I made an entire section for "intellectual" factors, while someone else might break down "love life" or "family" into half a dozen factors each) all comes down to personal preference. 1-3 could be why perfect happiness (or maximal subjective well-being) is unnattainable in practice. One more thought: if subjective well-being was condensed into a number and graphed over time, on reaching the end of the road there will be a maximum somewhere along the way. But you probably won't know where it was. On the plus side, not knowing lets you live as if the best is yet to come. And a question: does anyone know of a "happiness test" as well founded as the 5-factor NEO PI-R "OCEAN" personality model? For personality, I recommend Dr John A. Johnson's formulation of the IPIP-NEO test, based on the NEO PI-R which is the latest step in a slow convergence amongst personality researchers for the last 70 years. To know precisely what the factors are and which are lacking would tell one right away what is being neglected and what will be easiest to improve - thus netting the most happiness for a given amount of effort. I'm not formally trained in philosophy or psychology, raising the chance of making some whoppers of my own in the above. Corrections and further insights will be greatly appreciated.