A better formulation: Abstractions do not adequately describe the full working of a system. So higher-level approaches will always require a knowledge of lower-

A better formulation: Abstractions do not adequately describe the full working of a system. So higher-level approaches will always require a knowledge of lower-level operations. However, the opposing and terribly named "Dependency Inversion Principle" is true much more often: "High level [approaches] should not be dependent on low-level implementations."