Inheritance conflates code reuse ("avoid writing duplicate code") with polymorphism (allowing for multiple different instances to implement the same interface).

Inheritance conflates code reuse ("avoid writing duplicate code") with polymorphism (allowing for multiple different instances to implement the same interface). It also allows for trampolining method calls up and down a hierarchy (a method in a base class might call another method which might be overridden by another class in the hierarchy). Outside of OOP, we use composition for reuse and interfaces for polymorphism, and we don't trampoline method calls up and down a hierarchy because it's (probably?) always a bad idea. When we really need reuse and polymorphism, we can use both composition and interfaces, since the two are correctly orthogonal.