This just straight up isn't true for blue collar and service work.

I've worked those kinds of jobs with 12 hour shifts pretty recently, and you definitely Really Actually Literally Work 10+ hours of em'. It's kind of a buzz.

I could still do it, 6 days a week, day-in day-out at 32, which was pleasantly surprising to me as someone who has always struggled to work a good 4 actual hours of white collar shift.

Some jobs just come at you non-stop, and basically your only options are quit dramatically, or keep grinding through.

The camaraderie with your work colleagues is something too. I've never felt that kind of genuine, manic, expendables-in-the-trenches, darkly comic camaraderie in any white collar job.

There's something in it though, I wonder if it's just as simple as how 'physical' it is - if you're sort of 'exercising', obviously anything manual labour is, but also walking around, reaching up to shelves, etc. then it's more continuously doable. Tired and hungry sure, but doable.

I couldn't keep my brain continually engaged in SE for even what would be a short 'shift' - but I reckon I could still do the >12h full days I did at the cinema as a teenager (plenty to do even while all screens are showing).

I would say many white-collar workers are really only able to be productive a lot of the time for 4 hours a day, if they're lucky. I think it's more often far less for people. I don't think the majority of people are lazy, or burnt-out; I think there's just so much extra crap outside of their core tasks that it's very difficult for people to work on something that feels like they are honestly making something, or working towards something substantial.

Meetings, administrative tasks, emails, chat messages, more meeting requests, for most people the default setup has all of this coming at them like a firehose, and then bizarre expectations build and build like sedimentary rock into this seabed of constant immediate response times and work without productivity, a feeling of working with nothing at the end to justify it.

Depends on how you classify "productive"

in a 40-50hr work week I would say 50-60% is productive actual work (i.e writing a program, or doing the actual task you are paid to do), 10-15% is administrative (making task list, organizing your work, reporting about your work, etc) 10-15% is meetings about your work, 10-15% is socialization with co-workers, unofficial breaks, informal meetings, etc.

So if you do not count the other time as "productive" which I could and would challenge then that 4hr number holds true.

I don't know really. Several years ago, I got to visit Groupon HQ in Chicago (yes, really! :). I'm an 2nd generation computer person - I started using them in very late 70s and working professionally with them in the middle of the 80s, and even though I was a part of the .com boom, I've been away from that sort of world for decades. Wandering around that place for several hours my main though was "wow, how does anyone ever actually get any work done in this environment, which seems to be designed to encourage people to spend their whole day engaging with other people".

I once visited the opening of a new library, and found myself getting outraged when I looked around at the desks and sitting areas and places where one was supposed to be able to sit down and read a book ---- they were all totally exposed to visibility by everyone else in the entire room in such a way that I knew I could never be comfortable reading a book in this library. And that made me very angry. Yet the fault is somehow mine, as this FISHBOWL architecture is cool and all the rage. Guess I have to take the book home if I want to read it without being WATCHED.

You could also be a statistical anomaly with regards to how long you can work. If I were to bet, users of Hackernews have a higher focus time than most people right now, through training or otherwise.

I don't think this is true. First, as others have pointed out, you can absolutely do a full day of manual labour. I've done this myself before. The hardest day of my life was unloading 12 kitchens from the back of lorries and moving them across a muddy building site. I woke up at 6:00, got home at 18:00 and slept the instant I hit the sheets.

Secondly, we do work for more than 4 hours a day. In fact, I work in my sleep. The brain doesn't just shut off. The reason you can't just "keep going" at the keyboard for more than 4 hours is your hands are faster than your brain. But the brain doesn't stop. It keeps crunching away. Every morning I find myself with new insights and new ideas that I didn't have the day before. I'm not just being paid for the hours I spend bashing away at the keyboard, I'm being paid to engage my brain with the business.

I've always lived by "put the least amount of effort to achieve the most optimal results."

So using school as a for instance. If it takes me 12 hours of studying a week to ensure an A, but only 2 hours a week to ensure a B, is the additional 10 hours wasted studying really worth it? Nope. Much rather make my life more enjoyable.