Principles, Practices, and Processes are the basis of successful project management. It is popular in some circles to think that practices come before Principles.
The principles of management, project management, software development and its management, product development management are immutable.
What does done look like, what's our plan to reach done, what resources will we need along the way to done, what impediments will we encounter and how will we overcome them, and how are we going to measure our progress toward done in units meaningful to the decision makers?
This are immutable principles. These immutable principles can then be used to test practices and process by asking what is the evidence that the practice or process enables the principle to be applied and how do we know that the principle is being fulfilled.