Self-checkout was sold to the retail industry as a labor cost reduction tool and to consumers as a convenience upgrade. It has struggled to deliver either promise at scale, and the backlash — both from shoppers and from chains pulling the machines — reflects a miscalculation that was visible from the beginning. The premise required consumers to perform unpaid labor that workers previously did, while tolerating an error-prone system that flagged unexpected items in the bagging area, required attendant overrides on routine purchases, and created checkout lines that ran slower under volume than traditional lanes.