Sin causes a great deal of unhappiness in life. One common example is how sin causes us to be unhappy by wanting things.
It is not that desire for things is wrong, but often we are perfectly happy and then our sinful nature beings to fixate on something we want. Maybe the thing is out of reach or will take a while to obtain.
And now we are unhappy and there is no reason we should be unhappy. Often we are unhappy because we do not experience the good things around us because we are focused on what we feel we lack.
We do not really lack anything. Sometimes we need to have a reality check.
We are not unhappy because we lack, but because we are greedy. Often the greed is a cultural norm, but it is greed none the same.
God wants us to be happy. That is why scripture calls us to be content. True happiness is found ultimately not in material things, but in right relationship to God.