Why You’re So Tired Even When You Sleep Enough

To paraphrase John Mulaney, there are two types of people in this world: people who like to get to the airport “three hours early” and those who like to arrive at the last possible moment, and these people find each other and get married.

For too much of my adult life, I have pushed myself to be an early bird AND a night owl, all in the name of sweet, sweet productivity. My wife on the other hand is a sleep champion (at least her Oura ring tells her so all the time). I thought I was built differently. I was actually just running on a massive sleep deficit.

About two years ago, I started to become much more intentional with my sleep hygiene by minimizing screentime, using an eye mask (the sleeper hit), and tracking my sleep. All three helped in their own ways. Though I was recently reminded that fatigue isn’t just about how much you sleep. It’s also about what accumulates in your brain during the day and whether your daily habits are actually letting sleep clear it.

The reminder came through this video by Johnny Harris sent to me by Dave.

It’s 20 minutes, well produced and in my opinion well worth the watch. If you’d rather read, or just want to skim to the part that’s most relevant to you, what follows are my notes from it.

Your brain is running 300,000-year-old hardware

Here’s the framing Johnny uses: the human brain hasn’t meaningfully changed in about 300,000 years. Our ancestors needed that brain to make a handful of high-stakes choices per day, where to find food, whether to approach or flee, who to trust. The rest of the time was largely quiet.

Estimates suggest modern humans make approximately 35,000 decisions per day.

What to wear. Whether to answer that message now or later. What to have for lunch. Whether to accept the calendar invite. How to word the reply. Which tab to open. These feel small, and individually they are. But your prefrontal cortex, the region responsible for decision-making and executive function, doesn’t distinguish between “should I flee this predator?” and “should I reply-all?” It fires either way. And that firing has a cost.

The glutamate problem

Every decision your prefrontal cortex makes releases glutamate, the brain’s primary excitatory neurotransmitter. In the right amounts, glutamate is essential: it’s how neurons communicate and how signals move across the brain. But under sustained cognitive load, it accumulates faster than the brain can clear it.

Johnny points to what he calls brand-new research from the Paris Brain Institute. He’s upfront that it’s still being worked out exactly how the mechanism functions, but the core finding is straightforward: a full day of demanding mental work leaves a measurable buildup of glutamate in the prefrontal cortex by day’s end.

It isn’t just that you feel tired. Something has physically built up in the part of your brain you’ve been leaning on all day.

This is why you can be completely spent by 3pm without having done anything you’d call physically demanding. The fatigue isn’t in your muscles. It’s in your prefrontal cortex, and it showed up there one small decision at a time.

The caffeine trap

Most of us respond to afternoon brain fog with another coffee. It helps, for a while. Caffeine works by blocking adenosine receptors. Adenosine is a byproduct that accumulates throughout the day, and it’s your brain’s natural “you’re getting tired” signal. Caffeine blocks that signal, buying you a few more hours of alertness.

The problem: caffeine doesn’t clear adenosine, it only blocks the receptors. The adenosine keeps accumulating the whole time. When the caffeine wears off, all of that built-up adenosine floods in at once. The 2pm coffee that got you through the afternoon is part of the reason you’re still awake at midnight.

The nighttime half

Which brings us to sleep, and to why so many of us aren’t getting the kind that actually clears the day’s accumulated residue.

Sleep, particularly deep sleep and REM sleep, is when the brain does most of its metabolic cleanup work. Glutamate clears. Adenosine clears. The prefrontal cortex resets. But many of us are either cutting sleep short, or degrading its quality through evening habits that work directly against the process.

Johnny walks through his own typical evening in the video, and it’s uncomfortable to watch because it’s so recognizable. He gets home late, still has work to do, and pours a coffee to push through it even though his body wants to be in bed. Then some Netflix to wind down, which is its own stream of small decisions, which episode, whether to keep going. He’s not asleep until 2am. Each of those choices eats into the sleep that follows.

Chronotypes add a structural layer. Your chronotype, your genetically-influenced tendency toward mornings or evenings, determines when your body naturally wants to sleep and wake. Night owls who conform to a standard 9-to-5 aren’t sleeping too few hours by choice; they’re sleeping at the wrong time for their biology. The result is chronic, low-grade sleep deprivation that no amount of personal resolve fixes.

Blue light from screens suppresses melatonin, the chemical that shifts your brain from wakefulness toward sleep. As Johnny puts it, a bright screen at night fools your brain into thinking it’s still daytime, so it holds back the melatonin you need. You’re lying in bed, but your brain doesn’t know it yet.

Five things that actually help

1. Reduce daily decisions at the source

The most effective intervention is eliminating decisions before they happen. Meal prep on Sundays so lunch isn’t a daily question. Set out tomorrow’s clothes tonight. Create defaults for recurring low-stakes choices. Steve Jobs famously wore the same outfit every day, not for style reasons, but to eliminate one more daily deliberation. The logic holds even if you don’t take it that far: every trivial decision you remove in advance is prefrontal cortex capacity preserved for decisions that actually matter.

2. Time your caffeine

Johnny’s tip is to hold off on coffee until mid-morning, somewhere between 9 and 11am. The logic is about when the crash lands. Caffeine wears off after a few hours, so a cup first thing means the slump hits mid-afternoon, while a mid-morning cup carries you to the end of the workday before it fades.

3. Try a coffee nap

This is Johnny’s favorite trick, the one he calls one of the greatest things in the world. Drink a quick coffee, then lie down for about 15 minutes. A nap is when your body clears out adenosine, so by the time you wake the adenosine is gone and the caffeine arrives with nothing left to block, a kind of multiplier effect. It’s also worth noting Johnny’s point that cultures with a regular afternoon siesta show better brain functioning and, by one study he cites, a 37% lower risk of dying from heart disease.

4. Protect the wind-down hour

The hour before bed isn’t just “not working” time. It’s active neurological preparation. Dimmer lights signal to your body that the day is ending. Putting screens away removes both the blue light and the ongoing decision overhead that keeps your prefrontal cortex running when it needs to stand down. This isn’t deprivation; it’s giving your brain what it needs to do its job.

5. Know your chronotype

If you’re consistently sharp at night and groggy in the morning, that is not a discipline problem. It’s biology. Work backward from when you need to be at your best, protect your sleep window, and adjust what you can in your schedule rather than fighting your own nervous system.

What intentional living has to do with any of this

There’s a thread running through all five of these that I keep coming back to: every trivial decision you eliminate is energy preserved for a decision that matters.

Your capacity for thoughtful, reflective decision-making, about your relationships, your work, your values, the direction of your life, is finite. It depletes with every decision you make, no matter how small. The only way to protect it is to design your environment in advance so that low-stakes choices are already handled, and your best thinking is available for the things you’d say actually define you.

This is part of what we mean by intentional living at Holstee. Not minimalism as an aesthetic, or rigidity for its own sake, but the practical recognition that how you spend your cognitive energy over the course of a day shapes who you become over the course of a year.

It’s also why Reflection Cards exist, to offer a ready-made question for the moments when you want to pause, step off autopilot, and think about what actually matters. One prompt, one moment, without the overhead of figuring out where to start.

If you want a regular structure for that kind of practice, The Flourishing Life is our membership built around doing this work consistently, weekly reflection prompts, a community of people pursuing the same thing, and a curriculum designed to help you spend more of your energy on what you care about most.

Make it a good one.

— Michael Radparvar
Co-Founder, Holstee & Reflection.app

P.S. If you want to figure out your chronotype, searching “chronotype quiz” surfaces a few reliable options. Takes about five minutes, and the result might explain more than you’d expect.

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