I rewrote an internal tool from scratch to replace an old one that was being used by a few thousand people. It turned out that fully half of the users only eve

I rewrote an internal tool from scratch to replace an old one that was being used by a few thousand people. It turned out that fully half of the users only ever used it to see the auto-filled partial results that populated into one of the form elements. That particular requirement never made it into the specification for the new tool, and the rollout of the replacement did not go well, to put it mildly. In fact, there was so much of a mismatch between what these users thought the tool was for and what it seemed to be for from an engineering perspective that it was extremely hard to get any more specific feedback other than “The new one is terrible; I can’t get it to do anything”.