virtual functions must: Be overridden in every derived class. Have the same implementation in every derived class. Be declared virtual in the base class. Be declared virtual in every derived class.

Virtual functions are a cornerstone of polymorphism in C++. However, they do *not* need to be overridden in every derived class. A derived class can choose to use the base class's implementation if it fits the needs. The magic happens when you declare a function as virtual in the base class, allowing derived classes to override it if desired, creating a flexible and dynamic behavior. If you forget to declare a function as virtual in the base class, the function will not exhibit polymorphic behavior. That means calling the function on a base class pointer pointing to a derived class object will result in the base class's version being executed, which can lead to confusing results. Just remember: always declare in the base, override in the derived if you want that specific behavior!