Downcasting this to a derived type creates a dependency cycle. Derived types already depend on their parent type and the cast creates a dependency in the other direction.

Dependency cycles should be avoided as they make code both difficult to read and difficult to test. In addition, a type should not know about its specific descendants, even though it may impose some constraints on them as a group (for example, abstract classes may require every derived type to implement a method with a specific signature).