The notional eight hour work-day wasn't invented for occupations with high cognitive/reasoning workloads; it was invented for factories that needed workers to o

The notional eight hour work-day wasn't invented for occupations with high cognitive/reasoning workloads; it was invented for factories that needed workers to operate three shifts per day consistently. It became culturally ingrained because, back at the peak of labour-intensive industrialization, about 50% of the work force were employed in factories. But it doesn't actually bear any relation to how much time we can spend working effectively in tasks that require high-level reasoning skills. Nor does it bear any relationship to the earlier pre-industrial paradigm (agricultural labour from dawn 'til near-dusk, which could vary from 6 to 18 hours per day depending on the length of the day -- indoor lighting consisting of [expensive] candles). Unfortunately it's also easy to see whether a body is physically present or absent from an office -- easier than measuring the quality of its mental outputs -- and it's still relevant to service occupations, which is why we're mostly stuck with it.