“It is quite impossible to unite happiness with a yearning for what we don’t have. Happiness has all that it wants, and resembling the well-fed, there shouldn’t be hunger or thirst.”
Epictetus, Discourses.

Deciding to ‘be happy’ only when something that you desire comes to fruition is to delay happiness in the here-and-now. Yearning for something that is not in your control means that you forgo the happiness that can be had in the moment. And, as emotions are in the moment, then you choose to be unhappy because of the very choices you make. It’s like walking to the horizon to see the view on the other side…it never comes.