""Most people don't expect their house to burn down either but they usually have fire extinguishers.""
Not a good analogy. House fires are common and you expect something to catch on fire at least once.
Not one house in my neighborhood nor in the surrounding area has burned down or even caught fire. However, more than a few couples in the neighborhood have experienced divorce. This leads me to believe that divorces are more common than house fires.
I'm willing to bet that not one of those couples planned on getting divorced. Not one. But it still happened.
No one I know has ever had a housefire but almost everyone I know have at least one divorce.