While I’m quoting Stephen Prothero, this was a good column too:
What the world’s religions share is not so much a finish line as a starting point. And where they begin is with this simple observation: Something is wrong with the world. In the Hopi language, the word “Koyaanisqatsi” tells us that life is out of balance. Shakespeare’s “Hamlet” tells us that there is something rotten not only in the state of Denmark but also in the state of human existence. Hindus say we are living in the “kali yuga,” the most degenerate age in cosmic history. Buddhists say that human existence is pockmarked by suffering. Jewish, Christian, and Islamic stories tell us that this life is not Eden; Zion, heaven, and paradise lie out ahead.
So religious folk agree that something has gone awry. They part company, however, when it comes to stating just what has gone wrong, and they diverge even more sharply when they move from diagnosing the human problem to prescribing how to solve it.
Again, we see the belief in a lost Golden Age. This is one of the things I’m most grateful to Nietzsche for: all the time he spent elaborating on the theme that the only thing “wrong” with existence is that we are too limited by our selfish wants and fears to realize that you can’t have the good without the bad. We don’t all want the same things, and even when we do, we don’t want them at the same time or in the same degree. We don’t even agree on the same method for obtaining them. Conflict and challenge are inevitable. Suffering is inextricably woven into life’s tapestry.

The fundamental faith of the metaphysicians is the faith in opposite values. It has not even occurred to the most cautious among them that one might have a doubt right here at the threshold where it was most surely necessary – even if they vowed to themselves, “de omnibus dubitandum”. It might even be possible that what constitutes the value of these good and revered things is precisely that they are insidiously related, tied to, and involved with these wicked, seemingly opposite things – maybe even one with them in essence.

The tragedy of human existence is that we still have to live as if there is an essential difference, as if they can be separated.