I enjoy Sandi Metz' point there as well: Code just looking the same is not enough to call it duplication. Once you have to change two places looking the same to add a new feature or to fix a bug, then you have duplication and should centralize it.
I usually wait till 3; 2 is about the _very general_ point at which changing multiple places is about the same work as changing it to be centralized. 3 is almost always a better place to make that leap.
