The Importance of Engineering Principles

I think they're all very important. Dependency and version, it's very mechanistic. It says, make sure you depend only in the direction of abstraction. I call the other side the side related to main, the volatile part. Main is the most concrete of our functions. The things that violate the dependency and version principle all belong on the volatile side. That boundary line that I draw between the volatile and the non-volatile repeats itself several times in every system.