This video might make it sound like happiness is a bad thing. Like you're supposed to push yourself, never let up -- that itself is the truth.
I don't think that happiness is opposed to the truth. But happiness is a byproduct of a life that's aimed at the truth, a byproduct that helps you do what you need to do. Pleasure is a kind of psychic fuel. It can be hard to do without it. And pain often accompanies damage, and damage will hold you back.
But if you make happiness your goal, you will more than likely stop short of the truth. Why would you think you would find a thing if you stopped looking once you set your eyes on another thing? It might happen coincidentally, but wouldn't be more likely than that. Making happiness your goal might not even make you happy, and stopping at that goal rather than trying for something else might leave you both miserable and disconnected from the truth.