Oliver Burkeman, author of Four Thousand Weeks: Time Management for Mortals believes there is one hard-and-fast rule of time management that applies to everyone:

you almost certainly can't consistently do the kind of work that demands serious mental focus for more than about three or four hours a day.

This 3-4 hour range shows up in the routines of the famously creative.

• Charles Darwin: two 90-minute periods in the morning, declare "I've done a good day's work" at noon. After having lunch, a nap, and a walk, he would start another one-hour period.
• Henri Poincaré: did his hardest thinking between 10 a.m. and noon, and again between five and seven in the afternoon.
• G. H. Hardy: from nine to one would be immersed in mathematics, spending the rest of his time walking and playing tennis
• And many others: Thomas Jefferson, Charles Dickens, Virginia Woolf, Ingmar Bergman, as explained in Alex Pang's book Rest.

The lesson here is not to slack off once your four hours are up, and spend time watching the latest TV Show or scrolling Twitter.

It's about using whatever freedom you have over your day not to "maximize your time", but specifically to protect four hours of undisturbed focus, ideally when your energy levels are highest.

It's also to internalize the lesson that it's not possible to demand yourself more than four hours of high-quality mental work.

We're all living in a burnout society that demands too much of us, leaving no time for rest.

And we're becoming people who do not want to rest – who gets antsy when we don't feel like we're productive enough – pushing us beyond our limits, when doing less would've been more productive in the long run.

The valuable skill here to master isn't to push yourself harder, but knowing when to stop.

To resist the temptation of squeezing in a bit more work, and log off instead, go for a walk, read a good book, chat with your friends and family, pursue your hobbies, and actually live life.

And to know that you'll never achieve the feeling of "in control" or "on top of everything". And that's the reality of life.