Reduced to a Union - The Daily WTF
The code Clemens M supported worked just fine for ages. And then one day, it broke. It didn't break after a deployment, which implied some other sort of bug. So Clemens dug in, playing the game of "what specific data rows are breaking the UI, and why?"
One of the organizational elements of their system was the idea of "zones". I don't know the specifics of the application as a whole, but we can broadly describe it thus: