We all want to add behavior to a system confidently, and I have observed that my confidence in adding behavior depends on two factors:
I came across someone's analysis of this article at http://link.jbrains.ca/nHB3yz where Eugene, the author, worries that his students will find the steps I show here too small. I understand. I didn't start taking steps this small and deliberate until relatively recently, and in the meantime, I wrote code whose design I found reasonably inexpensive to maintain. Said differently, I don't know whether anyone can learn to program using this technique, but if it helps simplify their mental model of programming, and if it gives them a recipe to follow when they find themselves in doubt, then I'll feel like I've helped.