Many passengers are not aware that cruise ship itineraries are flexible and left up to the captain’s discretion. This means that cruise officials can choose to leave earlier or later than advertised, and can even modify ports of call. Though these changes are usually provoked by environmental factors, such as adverse weather conditions, itinerary changes have been taken for other reasons.
There are numerous stories of people who have been left by cruise ships, and many of the can be found online.
A recent Yahoo! News story discusses a couple who was left in Cuba. They believed that the ship would set sail at 5:00pm as advertised, but later learned that passengers were supposed to be on the ship at 1:30pm.
An infamous video on YouTube shows a distraught mother crying as the cruise ship leaves her behind, portside.