Workplace injuries from repetitive motion accumulate below the threshold of notice. No single keystroke, lift, or reach does harm, and the worker feels nothing at the time. What matters is the number of repetitions and the posture held while making them, neither of which is memorable. This makes prevention a matter of arranging the work rather than warning the worker: raising a bench two inches, or moving a frequently used bin within easy reach, prevents more injuries than any amount of instruction to be careful. The intervention has to be built into the workstation, because attention cannot be sustained for eight hours.