In computing, the robustness principle is a design guideline for software that states: "be conservative in what you do, be liberal in what you accept from others". It is often reworded as: "be conservative in what you send, be liberal in what you accept". The principle is also known as Postel's law, after Jon Postel, who used the wording in an early specification of TCP.

In the layered architecture pattern, each layer fulfills a specific responsibility and role within the application. Some focus on user interface logic, while others handle the execution of business rules. These layers complement each other's unique purposes, but they aren't explicitly reliant on one another to perform their own tasks.