Comment by Jtsummers

The rule of three is a guideline or principle, not a strict rule. There's nothing about it that misses the point. If, from your experience and judgement, the code can be reused, reuse it. Don't duplicate it (copy/paste or write it a second time). If, from your experience and judgement, it oughtn't be reused, but you later see that you were wrong, refactor.

In your example, it's about modularity. The directory logic makes sense as its own module. If you wrote the code that way from the start, and had already decoupled it from the writer, then reuse is obvious. But if the code were tightly coupled (embedded in some fashion) within the writer, than rewriting it would be the obvious step because reuse wouldn't be practical without refactoring. And unless you can see how to refactor it already, then writing it the second time (or third) can help you discover the actual structure you want/need.

As people become more experienced programmers, the good ones at least, already tend to use modular designs and keep things decoupled which promotes reuse versus copy/paste. In that case, the rule of three gets used less often by them because they have fewer occurrences of real duplication.