A 2003 study by Van Dongen and colleagues at the University of Pennsylvania placed healthy adults on six hours of sleep per night for two weeks. By day ten, their cognitive performance had deteriorated to the level of someone who had been awake for twenty-four consecutive hours. The critical finding was not the deterioration itself — it was that the subjects could no longer accurately assess how impaired they were. Subjective sleepiness ratings levelled off while objective performance continued to decline.

That gap between perceived and actual impairment is where executive performance goes wrong. The executive who believes they have adapted to five or six hours has not adapted. They have lost the ability to measure their own decline. And unlike a single night of deprivation, chronic partial sleep restriction creates a deficit that does not fully resolve after one recovery night. The ledger accumulates. The repayment schedule is far longer than most executives realize.

What Sleep Restriction Actually Does to Decision Quality