Even on terra firma, vacations can go wrong awfully quickly. The only saving grace is that, usually, you're not too far from safety. Mind you, at this point in history, cruise ships ought to be well and truly safe. They're massive things, floating cities, and armed with the best tech in nautical history. But to think that nature won't assert itself whenever it wants to is to invite trouble.
Just as a reminder, a ship recently ran into trouble on the high seas, and passengers got some pretty amazing video.