The text that was copied four times
transcript
Your app texts the customer four times. Placed. Accepted. Picked up. Delivered. Four handlers.
Handler one. Handler two. Fine. Handler three. Someone copied it, then edited by hand. Look at the wording. It drifted. Nobody decided that. It just happened, copy by copy. Four handlers. One piece of knowledge. And they disagree about it.
Now marketing wants a tracking link in every text. Four edits. And maybe a fifth copy, in a script, that you'll never find. Until a customer finds it for you.
Give the knowledge one home. One builder. The greeting and the order id are written once. Each status keeps only its own wording. The tracking link is one new parameter.
But here's the catch. Two discounts, both 10 percent today. Merge them, and they grow flags. Students go to 15. A sale excludes seniors. Different reasons to change. The wrong abstraction.
DRY is about knowledge, not lines of text. Ask: will a change to one always change the other?
Full breakdown in the lecture.