When you book a shore excursions, what are you getting? Or, more importantly, what are you getting yourself into?
For example, some of the most frail appearing Senior Citizens can run circles around me, so when I see they are part of a tour group I generally think nothing of it. Except on a tour of Valletta and Mdina, Malta... a walking tour. When the bus delivered us to the city gates of Valletta, a spry little woman informed the guide that her husband couldn't possibly walk the distance to the Palace of the Grand Masters. At that point it was apparent he'd never be able to handle the cobblestone streets of Mdina either. Unfortunately, the couple had either misinterpreted the tour description—clearly indicated as a walking tour—or overestimated their abilities. They also hadn't researched the port either, or they would have realized the streets are too narrow to accommodate a "city tour" on a bus.
Before going ashore, learn How to Read an Excursion Description.