As someone who understands human behavior, I have always believed that we are born with predetermined disposition. If you are a person who wakes up happy each day, you are lucky.  For people who wake up less than stellar each day trying to change your outlook in life is very hard.  Sure we can make small changes, but I don’t believe those changes can be modified to any large degree.

Look back to people you knew in grade school that you still might know today. Are they pretty much the same person?  I can confidently say your answer will be yes.  You likely won’t find a pessimist who is a blazing optimist, or vice-versa. Some people may have a situation or circumstance which caused them to be repressed, and is now removed and hence they show a different side, but it is not the norm.

While people go through some changes, overall people really do stay the same. And I believe it is hard-wired or genetic.

I consider myself neither a pessimist nor an optimist (though I tend towards optimism), but rather a realist. I tend to focus heavily on concrete facts and try to use that information to drive and motivate myself.