You are right, it is extremely rare. At face value, I know one couple who just pretty much resigned to staying together and they don't seem to be deeply unhappy, but aren't happy neither, and one couple I knew a bit less that seemed to have something genuinely nice going on. There was a lesbian couple I lost contact with years ago, they seemed happy too.

Now, marriages I knew what truly was going on behind closed doors? None. I'm not being dramatic, I really mean it, none, I don't know a single example of a lasting healthy, happy marriage - all of them are complete clusterfucks and most of the males are addicted to alcohol, drugs or cheating, regardless of class or income.