The document discusses coupling and the Law of Demeter principle, which states that objects should only communicate with their immediate neighbors. Following this principle leads to code with looser coupling, better encapsulation, and easier substitution of components. The document provides examples of correct and incorrect ways to follow the Law of Demeter when sending messages to instance variables, arguments, self, and newly created objects. It also discusses some exceptions like collections, as well as considerations around using accessors instead of direct instance variable access. Overall it emphasizes designing objects with complete interfaces that protect encapsulation.