It is a bit strange that in the 21st century, we start to talk about happiness again. You feel happy but you never possess happiness. Happiness is a straightforward emotional thing, not the index or whatever you can quantify.
Yes, it is true that happiness is not strongly correlated with money, but the weak association is statistically significant (to put it in a scientific way). It is hard to imagine that a poor man will feel any happiness if he suffers constant hunger, disease, and discrimination. Material possession, which can be quantified by the amount of money, is a sufficient prerequisite for the happiness, although it may not be a necessary condition.
It is important to distinguish the concept of joy and happiness. Joy is a sensation which is deemed to be temporally, while happiness is a long term feeling. Without money, there is no happiness, only intermittent joy. All the mishaps because of inadequate materials will gradually wear down the joyfulness.
However, the relationship between money and happiness is surely not linear. More money won’t lead to more happiness. It seems that the curve levels off after a certain point. Enough money, as many people claim, is good for them to enjoy the happiness. But the threshold for the “enough money†varies from person to person. Sometimes, the threshold moves up when people earn more money. For some people, they never earn enough money to reach the happiness.
Then the dissociation between happiness and money kicks in. Why do some people feel happier than others even though their material possessions are far less than those of others? A small and poor Himalaya country, Bhutan, gives an example of generally greater happiness with scanty material richness. It is the philosophy of life, the Buddhism, that enriches its people with spiritual support. Buddhism promotes low desire and peaceful mind. In fact, Chinese Daoism has written down the same thing before Buddhism: the strongest man is the one who has no desire.
Here we go. If happiness is nothing but satisfaction, then one may feel satisfied about what he/she has. But happiness is more than satisfaction. Happiness also relates to the equity. If there are other people who live better than you do, you will feel unhappy because you may feel unfair and want to live like them. This creates desire, a goal which will never be able to reach because there are always some people better off than you.
The key to happiness is to cherishing what you have, and enjoying you life.