The root of much unhappiness is comparison. Comparison gets in the way of healthy self-appreciation — and thus happiness – more than anything else. Because of comparison, hardly anybody is ever happy with what they get and nothing’s ever good enough for practically everybody. That’s because we measure our success in anything by comparing it to what others have or to what we have had before.
In other words, whether you are happy with what you get depends on how it measures up to some norm. That norm depends on two things: what other people get (social comparison), and what you yourself are used to getting (habituation). It is hard for success in any form (money, status, prestige, and so on) to improve your happiness because as actual success rises, the norm by which success is judged rises in step.