I see posts like these upvoted every so often on HN, HN is tech centric community but the rest of the world is not. 4 days work at same productivity as 5 day makes sense in tech centric community but doesn't make sense in factory work environment where more number of hours mean more work done. In factory work environment the only way to reduce number of days is to increase number of hours worked per day which might have other undesirable consequences.