We not only need to work happy, we need to work at being happy.
Positivity is such a high predicator of success rates.
Scientifically, happiness is a choice. It is a choice about where your single processor brain will devote its finite resources as you process the world.
If we study what is merely average, we will remain merely average.
Happiness is the precursor to success.
Success does not mean happiness. Check out any celebrity magazine to look for examples to disabuse you of thinking that being beautiful, successful or rich will make you happy.