The common trend is that married couples start off with some reassurance rituals to let the other know that you're still madly in love. Over time the rituals get abbreviated, but remain as a sign of reassurance. However they've become habit, even if there are problems they will be kept up.
Then when the problems get to be too much for one person, the other is blindsided because, "(S)he gave me a kiss and told me (s)he loved me every morning!" OK, (s)he did. But did (s)he do that because (s)he thought you expected her to, or because (s)he meant it?
(Disclaimer. I've been married for 22 years. My perspective is that if you don't know what can go wrong, you are left with just hoping that it will go right.)