There are some people who think that our happiness depends on the personality you are born with. Opposite to them, there are those who think that it is not a born question.
In life there are to many different factors which change our personality. For example, money. Obviously money does not make happiness, but it is also true that be poor could be a reason to be more sad than happy. Secondly, health. It is another important factor in life (and is relacionated (associated) with money somehow).
If you do not have a good health, you are heading to a worst life; it is a fact. Despite that, you can find people in the world who have not got good health and try to do their best in their pursuit of happiness.
To sum up, I think that whether you are happy or not does not depends on the personality you are born with, but on the factors which compose life. And the most important, it depends on how you deal with the negative factors that may come.