Of course, people are different and this is just an anecdote, but from my personal experience (a couple of instances) I can push myself to "fully dedicate" more than 4 hours a day of mentally really hard work - for some months. After that I tell politely that sorry, it is time for me to do something else for a while. More often than not, I have been welcomed back later. Of course, those have been exceptional circumstances, typically there is no need to fully dedicate more than 4 hours of mentally really hard work, but there is some less demanding aspects of the job taking some time off.
For how long can an employee, ever year, double his efficiency and the amount of customers he serves? That just doesn't sound sustainable.
>as a nation
Which nation?
So, as I said, I “had” an employee.
Let’s count in jobs. Basically a man fully dedicated to his job 37hrs/week creates about 1 new position a year, every year, because he makes the processes so efficient that we serve 2x more customers, so we can hire. That guy and another intern, they created -1 job in a year (his project brought literally no customer) and cost us 16k€ + his salary + the intern (I pay my interns, I give hefty bonuses to everyone).
I’m not complaining, it’s my job to root out the weed and prune it, and I did a mistake, but you need to understand, as a nation, how many jobs don’t exist because employees live off their colleagues (as for my share, I have created 6 jobs myself so I’ll just collect the huge margins, I’m just vexated he doesn’t collect his margins too). In sectors where everyone thinks it’s not their jobs, people end up harassing each other for the remaining positions. In growing companies, it’s the American dream with free food. The correct middle ground is to own your product for 37 hrs a week, and not delegate questions to be solved by the employer.