The word "happiness" is now used as a synonym for immediate gratification. Whatever feels good right now is what makes you happy. This fast food taco or this dose of heroin or buying a new video game or whatever it is.
There's an assumption that comes with this new form of happiness that says nothing "bad" will ever happen to you, as well. When happiness comes to you, it stays forever. Your car will never break down, you'll never be late for anything, you'll never be rejected by anyone, no one you know will ever die, etc. Of course these things will always happen to everyone, but when it happens to "happy" people, they lose their shit. They aren't prepared to deal with these things because they were under the assumption that they're "happy", and bad things can't happen when you're happy.
I agree that balance is what makes happiness, but happiness is more than just feeling good all of the time. It's a feeling of contentedness that comes with knowing who you are and knowing your place in the world, and being comfortable with that. And it means seeing various events and happenings as neither good nor bad, but just as what they are, and being comfortable with that, too.