They can sneak up on the leadership class of any particular country in very unexpected ways. They can cause all sorts of turmoil and angst. They can serve as the catalyst for governmental statements, rebuttals, rebuttals to rebuttals, and really, really angry rebuttals.
Of course, some foreign policy crises can be more serious than others. And the degree to which some incidents are allowed by a particular government to be raised to the level of a crisis says something about the degree of maturity possessed by that government.