It's not what they said it was.

When you begin a discussion, it has good intentions. You use the language that all the self-help books recommend and say"I feel" instead of "you" statements. You try to keep the conversation in the now instead of pulling out the old favorite zingers that always win. You make the attempt to settle an argument with the reality that you will never agree with the other person 100%. You realize that it's not about winning on your own, but winning as a team - i.e. coming to a mutual agreement/conclusion.
And then you get attacked. As if you were the one on offense.

Marriage is an attack on your entire person. When things get shaky it threatens your faith in the God that put you together. It trembles the idea of the entire institution that promised to provide you with a lifelong teammate.

I will never get divorced. I always said I would never get married, until I found someone from whom I would never get divorced. And now I wonder if I won't get divorced because I'm stubborn, or because it's the right match. Is there really a right match? Can two people live parallel lives and change according to both their environment and their partner? I suppose they can, if they're stubborn enough. But isn't it all supposed to make you happy?