Even people who would describe themselves as consistently happy can run into issues with a marriage partner.
We are different people, and some friction and disagreements are inevitable between people who spent a lot of years together.
It may be even truer now that we're living longer, and many of us are determined not to add to the divorce statistics compiled by our parents' generation.
Psychologist Daphne de Marneffe used the obvious phrase for her book title: The Rough Patch. The author tracks the stages of most marriages, and the challenges each presents.