* I usually have one or two major goals for the week, and four days to get there. I find it easier to reason about what I'm going to get done and how when there are fewer, longer days to work with, and I feel less interest in wasting time.

* I'm more comfortable focusing on days when I'm at work, and I'm more comfortable working a bit longer to get my stuff done, because I don't have to try to do my laundry and sweep the floors and get the groceries when I get home. (Although I realize it helps not having kids to look after, yet, so ymmv).

* I can do my dentist appointments and haircuts on my weekday off, so I rarely have to mess with my schedule or take off early.

* My weekends feel long enough. I always get back to work with a clear head. Mondays feel nice.

* I have not once told someone at work "nope, I can't do that, I don't have enough time." Will update if that changes :)

* I get to spend Friday hacking on personal projects when I feel like it. I haven't been able to do this in years, and sometimes it even benefits my employer. Free training!

I once worked at a place where everyone did a four day work week, and it was awesome. The big meetings were always on Tuesday, and we worked lengthy days (8:30-ish am to 5:30 pm), but that meant there was always room to do stuff right, without rushing. That includes taking time for tea.

They've apparently reported no drop in overall productivity, i.e. Four days' work is equal to the old five days work, an increase in productivity per day.

Plus on friday, people tend to be a lot less productive.

I agree with you, a lot of people in Silicon Valley are taking it easy one or two days at week while working from home, or leaving early while still pretending they are working 15 hours a day.

We should have a healthy debate about that

There's this strong concept of self-sacrifice as a way of ensuring company success. Sacrifice your life, sacrifice your friends and family for the sake of the company mission. It's only when people start demanding better hours and less abuse will a debate start to arise. And it likely won't be one with a respectful tone.

There is that whole narrative that was created that working in a startup/big tech company for long hour is really cool.

People are lying to themselves and to each other to fit into that narrative (Some are really working like crazy, but not the majority of the ones saying so).

I don't think it is going to change anytime soon.

It's an especially odd thing to say when you're all working on the same team, doing similar work: it kind of translates as "I'm so inefficient it takes me twice as many hours to do the same work as the rest of you! Go me!"

Also work is the only activity portrayed as useful and therefore meaningful, while spare time is expected to be filled with mindless entertainment.

I posit that it is, much like the trend toward open office plans (which have seen plenty of discussion, if not healthy debate).

It's an excellent way to protect yourself from actually having to work too much : always act and pretends like you're super busy. People will bother you less. My productivity increased a lot since I started acting busy to deflect non sensical requests and questions

Probably busy browsing social media and updating their pinterest. It's a lot more exhausting than people give it credit for.

It seems to me that the only way they could work a day less and not affect the companies productivity is if those employees did nothing during that day anyway. Say that in a work week an employee produced 100 units of work (feel free to substitute this with your favorite productivity microbenchmark). Thus, with the 5 day work-week each day the employee must produce around 20 units of work. Say you reduce that to 4 days, so now each day the worker must produce 25 units of work to be as productive. It follows that in order to work one less day per week the worker must work 25% more per day or overall productivity will suffer.

Imagine that your company implements something like this, suddenly per-day expectations go way up. Can you complete that meeting at 125% speed? Will your builds finish 25% faster? Can you increase your typing speed by 25%? Can you dig that ditch in 3 hours instead of 4? Can you clear tables 25% faster? I don't think anyone wants the consequences of this.

The only way I can remotely see this working out is for the employers of salaried info-workers in high profit-margin industries. For someone employed in a manual or skilled labor position it may be impossible or outright dangerous to attempt to complete tasks at 125% speed. I could however see this being a neat benefit that employers like the Silicon Valley types offer to outbid the competition, but I don't think this is practical for the economy in general.

An alternative would be that the 4-day schedule boosted employee efficiency by enough to make up for missing day 5.

Stress often degrades performance, particularly when it's chronic. I don't find it incredible that giving employees an extra day for their non-work duties/joys might increase their efficiency 20%.

Note that the employees must improve their efficiency by more than 25% for this to benefit the employer, and that they must do this every single day.

I can easily imagine that Monday mornings would be much more pleasant with a 4-day work week, but beyond that first morning I think it would increase stress. If every day I came to work knowing that my employer expected 125% out of me that day I think I would burnout much faster.

I think everyone who ever has had a tech job knows that yes, you can. Parkinson's law is a thing.

Another way to look at things is to use the 4-day week as the baseline. Add another day of work and people can only consistently perform at 80% without burning out.

Now, I'm not saying that I believe this is the case--that most companies can cut down to a 4-day week without hurting productivity long-term. Just that your argument isn't intuitive or obvious on its face, and I could see the data going both ways, or simply being a mixed bag.

This ignores the fact that employers don't pay you for how fast you run, but actually by how far you run in a day. Only the employee cares about how fast they can run.

Work is not divided into even units completed at a constant linear rate over the course of the day. It's a wide variety of different actions, and the time taken to complete each will vary wildly depending on tiredness, stress and morale.

Some tasks may take the same amount of time regardless, but some can drastically reduce. A well rested developer may realise the solution to a bug in a few minutes that would take them hours to solve on less sleep. Or indeed, avoid causing the bug in the first place.

You are correct, work is not distributed evenly throughout the day. But this doesn't matter to the employer. Your employer could care less how fast you complete a "days worth of work", all that matters is that each day you complete a "days worth of work". For employers of mostly hourly workers, this will change to an "hours worth of work", but the concept remains the same: the rate at which work gets done is unimportant next to the amount of work that gets done.

The criteria you give as affecting the productivity of workers is tiredness, stress, and morale, all of which I would assert decrease throughout the day. Wouldn't it then be more productive then for the employer to simply send the employee home earlier once they have lost their productivity? I think so, but employers would start to wonder why they ever paid for those non-productive hours in the first place, and that might have more sinister consequences for the worker.

It's not obvious to me that taking a day out of the work week is the best way to approach this. I think just talking with your employees to see how they're doing then adjusting their hours accordingly would be vastly more effective.

This sounds true to me, so let's assume that it is. If the average employee was unproductive for most of their day it stands to reason that employers would have a great incentive to only employ workers during their productive hours. Assuming the average employee is only productive for three hours a day, the employer is overpaying their employees by about 60%.

The problem seems to be how to eliminate the unproductive hours in a way that also benefits the worker. The way I see things working out is employers asking more of their employees for a smaller amount of compensation. Great for the employer, but I really don't think this is the kind of worker empowerment people are hoping for.

OR, if work-disrupting absences (appointments, etc) were all scheduled for the weekday off, rather than being distributed through the week and interfering with meetings, collaboration, etc.

You missed:

"Staff stress levels decreased by 7% across the board as a result of the trial, while stimulation, commitment and a sense of empowerment at work all improved significantly, with overall life satisfaction increasing by 5%."

or

"Employees designed a number of innovations and initiatives to work in a more productive and efficient manner, from automating manual processes to reducing or eliminating non-work-related internet usage,"

tl;dr: (Sometimes, maybe, for some time) decrease of work time is compensated by increase in productivity,

How you derived that tl;dr is beyond me, you can't just draw your own conclusions and call it a summary.