The loudest number from Britain's four-day-week trial was never burnout. It was that resignations fell 57 percent.

Across 61 firms and about 2,900 workers cutting their hours by a fifth on full pay, revenue held (up 1.4 percent) and 92 percent kept the policy. Now price a leaver: SHRM puts replacement at half to twice their salary, Oxford Economics at 30,614 pounds. Cut your resignations by more than half and the fifth day starts paying for itself. It was never a gift. It was the price of not burning people until they quit, a cost the old model paid all along, in churn, and never itemized. The caveat: this is desk work. Nobody has run it on a night shift or a hospital ward.