"Generic Software Design" as the author called it, is nice for setting the general direction of some implementation. This is why I like to read software engineering books. It's easier to solve a problem if you have some kind of framing to guide you. And it's easier to talk about the solution if everyone share the same terminology.

But yes, the map is not the territory, and giving directions is not the same as walking the trail. The actual implementation can deviate from the plan drafted at the beginning of the project. A good explanation is found in Naur's Theory of Programming, where he says the true knowledge of the system is inside the head of the engineers that worked on it. And that knowledge is not easily transferrable.