I think these rules of thumb are... okay. But I think it's more helpful to go back to how DRY was initially defined ("Every piece of knowledge must have a sing

I think these rules of thumb are... okay. But I think it's more helpful to go back to how DRY was initially defined ("Every piece of knowledge must have a single, unambiguous, authoritative representation within a system") and ask whether what I'm dealing with is actually "a piece of knowledge." There can be 10 identical copies, and if they just happen to be identical but they represent different things that might change independently, they should probably remain 10 identical, independent copies. Alternatively, if there are exactly two places something occurs in the code, but if they're out of sync the result is a broken system, you should think about unifying. DRY is too often treated as purely (or principally) syntactic, when that's actually much less useful.