Until the point of adding a new feature, the legacy code might not be a disturbance to the programmer's productivity. The codebase is in a state that is worse than desired, but the production systems work without any inconvenience.

Now is the time when the problems start to appear. The product owner (PO) wants to add a new feature.

For example, as a library manager, I want to know all the history for a given book so that I can measure which books are more in demand than others.