Why you’re so tired

Year after year, more people are quietly turning to the internet, asking the question, “Why am I so tired?” This growing curiosity reflects a shared but poorly understood experience. Every morning, many of us wake up feeling just a bit more worn out than we were the day before. The familiar afternoon slump has become so common that companies now joke about it, marketing products like coffee, energy drinks, or even food as solutions to combat our afternoon energy deficit. But what’s really going on? This isn’t just a matter of needing more sleep or spending less time on our phones before bed — although both are important. There are deeper reasons why so many of us feel constantly exhausted, and they’re rooted in the complex workings of our brains and modern lifestyles.

To understand why we feel so tired, we need to go back 300,000 years to the time of early humans like Johnny Caveman. Despite having a similar brain to ours, Johnny lived a very different life. His decisions were simple: where to find water, whether to hunt or gather food, or if the mushrooms he found were safe to eat. His daily routine was straightforward, with fewer decisions and less cognitive strain. In contrast, a modern human in 2024 wakes up to a barrage of decisions before even starting their day: finding their phone, choosing breakfast, planning the day, and managing countless other responsibilities. According to some estimates, modern humans make around 35,000 decisions every day, and this constant decision-making is taxing on the brain.

This mental overload is due in large part to how our brains process decisions. Each time we make a choice, a neurotransmitter called glutamate helps transmit signals between neurons. But as more decisions are made, glutamate builds up and begins to clog the system, making further decision-making harder and leading to mental fatigue. It’s like a city producing more trash than it can clear away, causing traffic jams that slow everything down. Even if we haven’t done any physical work, our brains can feel overwhelmed by the sheer volume of decisions we face daily.

While modern conveniences have reduced our physical workload, our mental workload has skyrocketed. Our brains, which evolved to make simple decisions in a simpler world, are not well-equipped to handle the complexity of modern life. This disconnect, known as “evolutionary mismatch,” explains much of the mental fatigue we experience today. Our brains are simply not designed for the high number of decisions we must make to navigate modern life. Solutions like taking naps, limiting decisions, or adopting routines can help, but it’s clear that we’re living in a world our brains haven’t fully adapted to.

Another key factor in our fatigue is the buildup of a chemical called adenosine, which signals our brain that it’s time to rest. Throughout the day, adenosine accumulates, making us feel sleepy. Caffeine, the world’s most popular drug, blocks this signal, allowing us to push through tiredness. But when the caffeine wears off, the adenosine floods back, contributing to the dreaded afternoon crash. One way to combat this is the “coffee nap,” where drinking a cup of coffee followed by a short nap can clear out the adenosine and give the caffeine a chance to work more effectively.

At night, many of us struggle with sleep due to our modern routines. Evolutionarily, humans evolved with different sleep patterns — some were night owls, others early risers, which helped groups stay safe by ensuring someone was always awake. Today, however, societal norms often force us into a one-size-fits-all sleep schedule, which doesn’t align with our natural chronotypes. This mismatch can leave night owls struggling to function in a world designed for early risers. Understanding and aligning with your chronotype can lead to better rest and less fatigue.

Sleep itself is crucial but often insufficient in the way we approach it. The modern world bombards us with bright screens, endless tasks, and caffeine, all of which disrupt our natural sleep cycles. To truly feel rested, we need to manage not just our sleep quantity but also our pre-sleep routines, avoiding late-night decisions and stimulating activities. The glutamate and adenosine that build up during the day must be cleared out during sleep, but without proper rest, these chemicals remain, leaving us feeling groggy the next morning.

In the end, the reasons we feel so tired are complex, but they’re rooted in a mismatch between our ancient brains and our modern lives. While we may not be able to completely change our lifestyles, understanding these factors can help us make small adjustments to feel a little less exhausted. Whether it’s limiting decisions, timing our caffeine intake, or aligning our sleep with our natural rhythms, there are practical steps we can take to fight this modern fatigue.

Year after year, more of us are quietly turning to the internet, searching for answers to a growing concern: “Why am I so tired?” It’s a question many of us can relate to, yet often find difficult to fully understand. Each morning, we wake up feeling a bit more drained than the day before. Our afternoon slumps hit harder, and it’s become so universal that companies poke fun at our collective fatigue, selling us products—be it food, drink, or even the idea of productivity itself—to remedy what feels like an energy crisis.

This isn’t another lecture on just getting more sleep or limiting screen time before bed. While those things matter, the reasons we’re all so tired go deeper. Our tiredness is influenced by what’s happening to our brains every day, in real-time. These small, constant interactions accumulate, shaping how well we sleep and how refreshed we feel the next morning.

To understand why we’re so tired, we need to rewind history back about 300,000 years. Back then, Johnny Caveman had a brain much like ours, but his daily life and decision-making process were far simpler. His prefrontal cortex, the decision-making center of the brain, wasn’t overburdened. Johnny’s choices revolved around basic survival tasks—gathering food, finding water, and maintaining his campsite. These were critical, but relatively straightforward decisions compared to the complex choices we face today.

Fast forward to the 20th century, where industrial life brought more decisions into play, yet still, not at the overwhelming level of complexity we experience today. Johnny Caveman, if transported into 2024, would now find himself making an avalanche of decisions, from mundane ones like what to wear, to more abstract and high-stakes decisions about work, family, and social life. By 8:30 in the morning, he would already be mentally exhausted, having made far more decisions than any of his ancestors. In our modern world, one estimate suggests we make around 35,000 decisions daily, with over 200 of those being food-related alone. It’s no wonder we’re exhausted.

You might think that with the conveniences of modern life—technology, machines, and comforts—we should feel more rested. After all, we’re no longer running from tigers or hunting for food. But the truth is, our brains are wired for survival in a simpler world, not for the constant barrage of information and decisions we face today. This leads to what scientists call an “evolutionary mismatch,” where our caveman brains are living in a modern world that exhausts them.

When we make decisions, neurotransmitters like glutamate help transfer signals between different parts of the brain. However, as decisions accumulate, glutamate builds up, causing the brain’s system to become clogged, making it harder to think clearly. This leads to mental fatigue, similar to how a city’s roads would become blocked by trash if not cleared regularly. In modern life, this “mental trash” piles up quickly, leaving us feeling drained even if we haven’t done any physically strenuous work.

To combat this, many cultures have embraced solutions like bifasic sleep, or afternoon naps, which help clear the mental clutter and reset the brain. Studies show that people who take regular naps not only function better mentally but are also less likely to suffer from heart disease. However, in hustle-focused cultures like the United States, the idea of taking a nap in the middle of the day is often stigmatized, contributing to a collective feeling of exhaustion.

In addition to decision overload, another chemical called adenosine plays a significant role in our tiredness. As we go through the day, adenosine builds up, signaling to the brain that it’s time to rest. But caffeine, the world’s most popular stimulant, blocks this signal, tricking our brains into feeling more awake than we really are. Eventually, the caffeine wears off, and the adenosine floods our system, resulting in the infamous afternoon crash.

One effective way to combat this is the “coffee nap.” By drinking coffee and then taking a quick 15-minute nap, you allow your body to clear out the adenosine while the caffeine kicks in, leaving you feeling more energized afterward. Timing your caffeine intake, such as drinking coffee between 9 and 11 a.m. instead of first thing in the morning, can also help manage your energy levels more effectively throughout the day.

So, why are we so tired? The answer lies in the way our modern lives conflict with the biological design of our brains. From decision overload to disrupted sleep patterns and the misuse of caffeine, our caveman brains are simply not equipped to handle the demands of the 21st century without feeling fatigued.

Ultimately, there are ways to mitigate this. Limiting decisions by planning outfits for the week or meal-prepping on Sundays can reduce mental clutter. Understanding your chronotype—whether you’re a night owl or an early bird—can also help you align your schedule with your body’s natural rhythms, ensuring better quality sleep. And of course, making time for rest, naps, and proper sleep hygiene can go a long way toward fighting that ever-present sense of exhaustion.