The requirement that disappeared
In the robot cell workshops, the customer's IT manager asked for automatic recipe download from the MES. Everyone nodded, and it was written in the minutes.
Six months later, at the factory acceptance test, the IT manager asks: “Where is the MES download?” Nobody designed it. It was in the minutes, but it never reached the design specification.
Requirements are not lost because people are careless. They are lost because there is no thread connecting each requirement to its design, its test and its acceptance. That thread is the traceability matrix.