Failing to meet your own expectations is not the opposite of happiness. Your ability to fail and still appreciate the experience is key to happiness.

The joy is not in getting what you want, but the process of working towards it, then raising the bar, and doing it again. If you fail, learn from it. 

We don't always need to be positive, even if that is constantly marketed to us. We will have trouble. Things go wrong. People upset us. Mistakes are made that make us negative. It's all part of life.

Negative emotions are necessary, but we need to learn to express them in a socially acceptable way that aligns with our values.

Raising a child makes us happier than beating a video game. Completing a marathon makes us happier than eating chocolate.
These activities involve pain, struggle, even anger, and despair. But once you have completed them, you look back and feel happy because these kinds of events allow us to become our ideal selves.

Achieving a difficult long-term goal makes us happy. But once you reach the goal, there will be another thing to pursue to make you happy.

That is because our ideal self is always a few steps away from us. What matters is not that we achieve the plateaus of success, but that we're continually moving towards them.