Why must the value chosen for a sentinel be carefully selected?

The value chosen for a sentinel must be carefully selected to ensure it does not overlap with valid data values, which could lead to incorrect program behavior or logic errors. A sentinel value acts as a marker to indicate the end of data or a special condition, so it should be easily identifiable and consistent throughout the program. Additionally, using a well-defined sentinel can enhance code readability and maintainability, making it clear to other developers how the control flow operates.