Modularity.
Each component in your system should be a (relatively) simple composition of other (smaller) components, in such a way that each component can be understood as a black box, and is interchangable with any other implementation or the same thing.
> All too often, we end up creating lots of shallow modules, following some vague "a module should be responsible for one, and only one, thing" principle.
This is what I'm talking about: this writing is too smart for me, because I can't take any simple answers from it like "modularity" without feeling another part of the article contradicts it with other smart sounding ways of saying don't listen to smart stuff.