Happiest Pessimist

I walk with an upbeat, with something doubtful in mind. It's like I can't be happy as if it's a crime. I fill my cup with life until it's half empty. They ask who am I? I'm the happiest pessimist that you ever done see. They say what goes up must go down. But if I'm so up and I'm so down... Where do i go now? If there isn't a clear place than what am I to do? Oh. Who am I? I'm the happiest pessimist that you ever done see. Being happy scares me, being low-spirited comforts me but in comfort I find happiness which becomes discomforting. You asked who am I? I'm the most bitter optimistic... I mean happiest pessimist.. I'm the most common teenager that you've already seen.