I've known a lot of couples that broke up. A lot of them that married usually had similar values and morals; similar backgrounds (same college, had the same friends, same ethnicity, religion, etc.) To get to the point of marriage in the first place, for the majority of people, they were similar -- even with respect to attractiveness and facial features.
There was one feature that I notice 90% of the time when the marriage did not work, the woman thought that the "relationship got stale", "there was no spark", etc. They could be 99% compatible with respect to values and morals; but if one of the person in the marriage didn't respect the vows.. didn't respect the institution of marriage; they would get divorced.
People say a lot of things, but it's their actions that count. People say they will "stick it out through sickness and health; through wealth and poverty"... but a lot of times those that get divorce don't really understands what that entails. They don't fight for their marriages.
Perhaps it's my social circle (I'm middle class to upper middle class; everyone of my friends have a degree from a reputable college), this has been the case for most of the divorces I see. On paper, almost every divorce shouldn't happen because they matched so perfectly.
Next person I marry (if I marry), must understand the fact that relationships are hard, you gotta fight for it or else it wouldn't work regardless how "compatible" the relationship seems.
ps. One of my good friend's advice who has a loving marriage told me they agreed to have sex on a certain day REGARDLESS how each other felt. Even if they we tired because of work... just didn't feel like it... or etc... etc.. They had sex. I think he said their day was on a saturday. They are still in love with each other for the past 10 years.. .So yeah, next girl I meet, that's going to be on the agenda. Trust me, as a guy there will be times you don't want to do it, but according to my friend, you just have to. I think it makes sense.