Now, before everyone digs out their old goth clothes and screams, "Aha! We told you that the world was just an endless black ocean of suffering!" that's actually the opposite of the point we're making. It appears that the reason so many people profess to be miserable is specifically because they think they're missing out on some magical emotion that "happy" people feel all the time. They're tormenting themselves over the loss of something that nobody actually has, because that thing doesn't even have a definition.
See, the thing is that humans have never actually settled on what "happiness" is. A historian named Darrin McMahon exhaustively studied how happiness has been viewed over the last few thousand years and found that it was constantly changing.
"I'd say I define happiness as less than three types of lice on my body."
Go back to ancient Greece and it's very simple: Happiness = Luck. Either the gods dribbled their joy juice on you or didn't; either way, there was nothing you could do about it. And that was it, end of conversation. It was nothing to get upset about. In fact, in every European language, the root of the word for happiness is some older word that meant "luck." Ours comes from the old Norse and Old English word "hap", and hap simply means "luck."