The 40-hour workweek was introduced by Henry Ford in 1926 when most people performed physical labor in factories.

Back in those days, productivity was linear:

- 1 hour worked = x amount of goods produced
- 8 hours worked = 8x amount of goods produced

But in today's knowledge economy  -  where most of the work is done with our brains  -  productivity is no longer linear.

Today, our productivity depends on our level of focus, mental clarity, energy, and creativity. These factors aren't constant  -  they fluctuate throughout the day.

That's why we are highly productive during some hours, but can't seem to get anything done during other moments of the day. 

Although it can differ from person to person, multiple studies found that the late morning tends to be the most productive time of day for more than 75% of the workforce.

The afternoon, especially the two hours after lunch, is usually the least productive time for most people.

Recent neuroscience shows that cognitive performance tends to be best in the morning. That's when we can focus better, think more clearly, and solve difficult problems more easily.

As Dr. Michael Breus, clinical psychologist and author of The Power of When, wrote:

"On average, the peak time for cognitive functioning is about two to four hours after we wake up. This is when our body temperature starts to rise, which boosts alertness and mental focus."

As the day progresses, people get considerably worse at absorbing new information, planning, and resisting distractions.
The reason this happens is biological.

Our bodies run on a circadian rhythm that affects hormone production, brain wave activity, and body temperature.

Each of these factors influences our energy level, which impacts our mental focus and productivity.

In other words, use the first hours of the day to work on the most challenging tasks that require optimal focus, mental clarity, and brain performance.

Research shows that our willpower (or self-control) tends to weaken as the day progresses. 

We make dozens (or even hundreds) of decisions throughout the day. Eventually, this leads to decision-making fatigue, which drains our willpower.

As Roy F. Baumeister, professor of psychology and author of Willpower, said:

"The more you use your self-control, the more it gets depleted, making it harder to exert control as the day goes on."

In other words, if you need to get an important task done, do it early in the day before your willpower is drained.

When you schedule challenging tasks for later in the day, chances of getting distracted or procrastinating on your work are much higher.

Working in synchronization with your body's natural clock is the key to unlocking peak productivity. That's why one of my core productivity rules is to use the morning for making and the afternoon for managing.

In the morning, when I'm at my most productive, I schedule 2–4 hours to work on making-type tasks, such as:

These making-type tasks usually require the most willpower, focus, and mental energy, so the morning is the best time to complete them.

In the afternoon (especially the two hours after lunch), I'm at my least productive. Compared to the morning hours, my brain seems to function at a fraction of its potential.

That's why I use the afternoon to work on managing-type tasks, such as:

Managing-type tasks generally don't require maximum brain performance or high levels of willpower, so I can easily do them when I'm not at 100% capacity.

In today's knowledge economy, the timing of your work matters much more than the total time you work.

By scheduling high-priority, complex tasks during those hours when you perform at your best, you can work smarter and maximize productivity.

It's important to protect your peak productivity time and treat these hours differently than 'ordinary' work hours:

By scheduling according to your 'chronobiology,' you can achieve far more in a fraction of the time.