"Tax and Import Duty look the same, so we should extract this into a shared utility."

But they are not the same thing.

Invoice Tax and Import Duty represent completely different business rules.

Today they just happen to share the same formula.

6 months later…

- Tax: category-based rules

- Import Duty: country-based rules

Now the shared abstraction becomes a bug factory.

✅ DRY is about knowledge, not code

Tax and Import Duty represent different business rules, so they stay separate.

Same implementation. Different business rules.

6 months later…

- Tax: category-based rules

- Import Duty: country-based rules

No shared abstraction to break.

No unrelated changes forcing each other.

No accidental coupling.

Full article: journal.optivem.com/p/d…

------

Join 5,400+ engineers: journal.optivem.com