I think the only reason people ever gravitate toward negativity is because that is how they have been conditioned growing up.

If one has only been shown, by parental figures and the society they have grown up in, how to operate from a negative perspective, then until something or someone comes into their life to jolt them awake to the realization that there are other possibilities and choices, they will continue to operate from that negative perspective.

I think when there is a strong desire for a change and a deeper knowing (albeit an unconscious one) that the negativity is just not right - a new awareness is made available and opportunities for positve growth make themselves presentable; or rather one begins to perceive those positve growth opportunities where they couldn't before.

My guess is that depends on one's temperament, meaning his inborn qualities. Michaela is right about the external influences, but character we are born with greatly matters (unless you believe in John Locke's tabula rasa :). For example if one has natural tendencies to be nonconformistic, he won't accept the way society restrains our thinking.

The same is with pessimism. I have a friend that is very, very pessimistic person. Even though she is clever and beautiful, she sees the world in dark colours. There is no way to convince her she is wrong. So her disadvantage is not only being a pessimist, but also the fact that she doesn't want to change. In her case, this is because she has a deep rooted low self esteem and she isn't self-confident.

My mom often says about my vices: "if you are like that, why don't you change?" But we cannot change just by thinking differently. There are many emotional barriers standing before us, blocking us from acting not like that.

I just want to say that there are several layers to a negative person's character. Some people are just meant to stay negative. Trying to convince them is useless as there are a bunch of people that want to change, but don't know how. It would be better to focus on them.