I agree with what a lot of people are saying, that marriage is a commitment and they take work and aren't always easy or fun. I think a lot of people just give up on them after a while, and I think that's sad, but I do think there are instances of where a marriage simply will not work no matter how much effort you put into it.
My parents have been divorced since I was about 6 years old, I believe, and they were seperated years before that. I only have two memories of my dad still living with us and one of them involved my mom crying. As a couple they just didn't work. Constantly fighting, my dad had temper problems and his drinking didn't help matters any and I don't think it was until my mom left him that he even seriously considered getting help. Neither of them were happy while they were married and it made us kids miserable, too.
It seems that after they separated, their relationship improved a lot. They still fought sometimes, but they could keep it away from me and my siblings more and they usually worked things out again. They've remained friends to this day, and we've always done things like holidays and birthdays as a family, so I don't feel that I really missed out on either of them as parents. I know that growing up with them still trying to make their marriage work would have been very different, and I really think it was best for everyone that they got divorced.