The way I've heard Sandi Metz talk about it is basically that Don't Repeat Yourself isn't the important thing, but it's what we tell beginners who don't realise

The way I've heard Sandi Metz talk about it is basically that Don't Repeat Yourself isn't the important thing, but it's what we tell beginners who don't realise that having 15 copies of the same logic all over their program isn't a good idea. It's a proxy for the idea of abstraction, because that takes much longer to develop a good taste for. And unfortunately, a lot of people learn the quick reminder "Don't Repeat Yourself" without ever hearing the actually definition of the principle: "Every piece of knowledge must have a single, unambiguous, authoritative representation within a system", which doesn't roll off the tongue as easily. The DRY principle is a bit easy to corrupt and mis-apply, if you don't ever learn what it really means.