He noticed when a technician on a call began by examining copies that had been thrown in the trash and deduced from them that the problem with the machine was different from what the customer had reported. “The trashcan is a filter between good copies and bad,” one technician explained “Just go to the trashcan to find the bad copies and then… interpret what connects them all.”
If you want to investigate what’s going wrong, or what someone is trying to do, you can investigate the record of the attempts/edits they’ve made. Sometimes that gives a better understanding than even they can explain themselves.