Maintaining a romantic bond for years on end is challenging, but adding kids to the mix and keeping a romantic connection the entire length of the relationship is extremely challenging, if not impossible (even with all the great advice books out there on the topic).
Every parent, if they're honest, will admit that a particular stage of parenthood was especially challenging. For me, it wasn't infancy. It was hardest for me when the kids were in that in-between stage.
Most of us marry with the best of intentions. Sometimes that just doesn't work out. We shouldn't slap a #fail label on people who divorce. Let's have faith that they'll do things better the next time -- or maybe the time after that.
I do not believe that couples ought to stay together for the sake of the children. Marriage is not a prison sentence; children are not your jailers. But that does not mean that divorce does not scar kids.