[Dracophoenix]

There are many good marriages in which at least one spouse brags about a happy (however that's defined) life of 20+ years and many bad marriages that aren't evident as such until the inevitable "he/she left me and I don't know why" post on Reddit.

I agree that it is important to take a person's examination of his/her self or his/her (ex-)spouse with a grain of salt. And while people are blind to their own faults, you're making the mistake of thinking that divorces are based on falsifiable and rational assessments. Some are. Some aren't. But one isn't likely know the true reason a long time after the fact, if at all.