It's not a question of happiness, it's a requirement. Consider the alternative.
Smile, it's better than a poke in the eye.
No one can drive us crazy unless we give them the keys.
If food were free, why work?
Happiness in the present is only shattered by comparison with the past.
Search for meaning, eat, sleep. Search for meaning, eat, sleep. Die, search for meaning, search for meaning, search for meaning.