If this were entirely true, businesses wouldn't be open from 9am-5pm but would have three 8-hour shifts throughout the day and run 24/7 and simply outcompete co

If this were entirely true, businesses wouldn't be open from 9am-5pm but would have three 8-hour shifts throughout the day and run 24/7 and simply outcompete companies that are only open 9-5. The "best" companies would have even longer shifts and more complex schedules, with fewer employees. 9-5 isn't the 'optimal'. It's simply what is 'most common' for a diurnal society. Nobody is driving around town looking to get a hair cut at 3am and staring at an IDE from 1pm-5pm trying to solve a bug isn't making you any more efficient than thinking about the problem while cooking an early dinner. Humans do suffer fatigue - both mental and physical - and proper lengths of rest helps both kinds. I posit that happier employees are more likely to trend their work/life balance in favor of work if they enjoy their work and enjoy their company. Unhappy employees will skirt by on the bare minimum required knowing that hiring/training a new employee isn't worth the cost of firing them.