what are you hoping for?

From a conversation with Kaitlyn today, paraphrased.

"I think you have to let yourself be happy. I spent a lot of high school determinedly unhappy, because that's 'who I was' at the time. But it's just as fake as pretending to be happy. I always thought I was a pessimist. But now I think that might never have been true, I just didn't let myself think otherwise."

I've been thinking about that recently. What makes someone an optimist or a pessimist? Are you born that way, taught that way? Think that way to fit in? Is it really as simple as half empty or half full? Is it about outlook or choices or situation?