Work for only 3 hours a day, but everyday

More specifically, it was arrived at as a target for labour rights campaigners after the 10 hour day had started becoming common. Owen formulated the famous "eight hours labour, eight hours recreation, eight hours rest" slogan in 1817, but it took half a century for the 8 hours day even to become the main goal for labour organizations most places (because they were still fighting for the 10 hour day, or even the 12 hour day), and it took more than a century from Owen's slogan for the 8 hour day to become widespread.

Since then labour organizations in many countries have set goals for shorter work days, and many countries have seen the work days shortened further to various extent, but given how long the fight for the 8 hour day took, we can expect it to take a long time.

But as you say, it has absolutely nothing to do with 'optimal'.

Such a regimen would kill those who immediately jumped into it from a typically sedentary life, sure. But if eased into, there is no reason most people couldn't handle it. Elite athletes didn't become highly performing in a day, and there are no special biological qualities required to become a high performer. It's just a lot of work, and most prefer to not do that work.

You don't know his baseline personality/attitude. It might be he's good at the relaxing and being creative aspect, and so needs to personally remind himself to work hard. Other people might naturally work very hard, but need to remind themselves to relax.

it's an assumed 8 hour day... if they notice you're only working 4 hours they'd expect you to bill half a day

Thanks.

I don't see how the Einstein example is relevant, feel free to elaborate.

On instagram... you're introduction valuation, not nominal productivity.

i.e., imagine I can either produce 1 smartphone after a year working 100 hours per week, or produce 100 smartphones after 10 years, working 10 hours per week.

Well, nominally, the latter example is way more productive. You produce 10x as many phones per year while working 1/10th the time. There's absolutely no way you can say that the former is more productive.

But, building today's smartphone in 10 years is obviously going to leave you with little value. In 10 years, your 10-year old tech will be valued very little.

Your instagram example is like that. The engineers working on it may have been much more productive if given 10 years to work on their project, but its valuation would be shit because it's last to market instead of first to market. So, not a great example.

If you're trying to say that working hard in short periods, allowing you to get to market before anyone else, is better than taking your time, then obviously that's true, but that's more a function of competition than it is of productivity!

Further, it's a poor example. Show me data that's meaningful for a large group of people, not extreme outliers. How many people do you know that created a $1b company or came up with g relativity theory? It's like saying 'dropping out of school is a great idea, look at Gates and Zuckerberg'. When in reality the data overwhelmingly supports the notion that finishing school has positive outcomes in your life. You can prove anything by looking at selective (outlier) examples, but show me examples that commonly occur.

Meanwhile overwhelmingly studies show that productivity drops sharply after some amount of hours. You get more work done per unit of time when working 8 hours per day, than 16 hours, period. That's what productivity measures.

There is obviously some lower bound, if you work in 3 minute intervals you're spending a lot of your time 'starting up' your workspace and getting your brain tuned in your work, and so productivity (work per unit of time) drops. I wouldn't be surprised if 4 times 90 minutes was less productive than working for 6 hours, that makes a lot of sense. But there's also an upper bound, where you lose concentration and motivation and are better off resting and getting back to it the next day, such that working two days of 6 hours is more productive than a single 12 hour session. Feel free to look at the many, many studies that confirm this. The above applies to virtually anyone, any organisation, any individual, productivity has diminishing returns as you scale way down or way up.