One of the ways I like to look at it is that I'm a foreman and one of my construction workers can't show up, and I need a substitute, I don't want someone that

One of the ways I like to look at it is that I'm a foreman and one of my construction workers can't show up, and I need a substitute, I don't want someone that is even less useful than my worker. A really good substitute is someone that can do everything that my original worker could do, and maybe then some even if I don't take advantage of it. Meanwhile, I don't want his results to be worse than my original worker's, but I sure don't mind if it's better. In other words, if my original worker only knows how to turn a Dog into a Dog, and that was good enough, the most useful substitute is someone who can take any Animal and turn it into any special kind of dog. Or maybe I care about 2x4's, and my normal guy only knows how to turn Cherry into 2x4's and isn't trained on anything else, even though that suited my needs. The best sub is someone who can take lots of kinds of wood and turn it into different kinds of posts and planks; I'm just only taking advantage of his 2x4 skills. Unfortunately a lot of programmers design subclasses by saying "hey look, I'm good at starting with a schnauzer" or "hey look, I'm good at starting with Brazilian cherry". These guys aren't helpful when they show up in your parameter list.