Whenever interface operations commute, they can be implemented in a way that scales

I ran into a deep review of a paper on scaling Linux, and I realized that the commutativity rule explains why REST and functional programming blew away enterprise architectures on the web. Yes, because REST scales, but this is the first real explanation that I have read of why that is, and the first I've heard of the scalable commutativity rule.

The review is worth trudging through, I've just started reading the paper.