People are pessimist because of intelligence and optimist because of will. You can't just be one, better be a combination of them.

The Optimist sees things were others say there's nothing. We're wrong or right when we are the only ones saying that some things are possible or real?I guess, by the end of the day if we are happy it doesn't matter if our truth is not absolute.

I think being optimistic means being content with what you are given. Pessimism comes with unreachable desires. You'll become a pessimist when you will not reach all those great purposes you dream about. Life can't be what you want it to be. You can't always get everything you want. One should not be greedy. But who can resist the temptation of always wanting more?   

I believe pessimism is like a warm blanket; you'll never get hurt if you don't have great expectations from the start. Many don't agree and say that pessimism is an excuse for not trying and a guarantee to a personal failure. But then optimism could be about being blind or about pretending. We decide in our minds that things are ok and we are happy. But, in reality, things don't change only because we want them too. Everybody is optimistic at times, just as none can't help but feel pessimistic about things during some moments in life. Self-delusion is hard to live sometimes.
  
They say that a pessimist complains about the wind and an optimist expects it to change but neither does anything to make sure it will change, while a realist just adjusts the sails… In conclusion, I'm definitely a realist. In my opinion this is the only way to achieve something: not being blinded by either optimism or pessimism.