The hope and optimism is fueled by the caffeine, and the ability to think, and the willingness to put one foot in front of another. There's also the prospect of change: change your ways, change your diet, change your hair, change your brain.
The new day might seem like the old day, but it's not. And you might seem like the same old being, but you are not. And as long as you breathe, you can grow, and morph, and move. That's everything in a nutshell.