You often refer to your flexible cruising schedules What does this mean?

You often refer to your flexible cruising schedules What does this mean?

With expedition cruising, no two voyages are the same. The itineraries we provide are simply a guide. The actual sailing and landing programs must be created by the expedition leader and captain at the time of the voyage, since the changing ice, weather, and wildlife conditions of the polar regions always determine what is possible for us.