From Douglas Adams' The Hitchhiker's Guide to the Galaxy:
“This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.”
I've recently begun re-reading this book (after having previously read it when I was 12 years old). It is a gold mine.
Many problems can, when viewed from an uninterested third-party's perspective, be whittled down to obvious insights.
Why are we, as a species, generally unhappy? What does it even mean to be happy or unhappy? From the trenches, we can overanalyze things and say it's due to inequality, racism, religion, capitalism, and everything in between.
But viewed for what it is at its most basic level, we are unhappy because, well, consciousness is a bitch.
Humans have only very recently figured out that, by using technology and language to stockpile resources and build institutions, we don't have to live from meal to meal.
But there's a lot of other stuff we haven't figured out. God? The Universe? Renewable energy? Anger? Fear? What? Our descendants (assuming we don't cause Armageddon before then) will laugh at how primitive we were.
Our brains haven't evolved fast enough. They haven't caught up. And so we are ill-equipped (at least for now) to deal with higher thoughts.
To put it in very corny terms: if the history of the world is the School of Knowledge, we're just entering our sophomore slump. It's the uncomfortable realization that we aren't the hot shit we thought we were, and that there is an infinite amount of things we don't know.