5 Ways We Make Ourselves Less Intelligent Each Day

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When it comes to psychology, we’re often our own worst enemies, and that goes double for our effective IQ.

The concept cares less about abstract numbers and focuses entirely on what we actually get out of our brains. It is a practical blend of cognitive performance, executive function, fluid intelligence, and the real-world application side of intelligence, harking back to what Sternberg might call “successful intelligence.”

When we zero in on the practical choices that either sharpen or dull our thinking, we see just how much of the outcome is in our own hands.

Self-sabotage is nothing new, and steering ourselves towards smarter habits starts with naming what’s holding us back. In that sense, self-awareness is the best antidote—which is why here, we'll take a walk through the rogues’ gallery of mental missteps, starting with five of the most common repeat offenders that keep us from being the best versions of ourselves.

5 Major Mental Mistakes Too Many of Us Make

1. We don’t treat the brain as a muscle to train.

By far the most performance-reducing habit is treating the brain as if it’s a fixed fixture. Psychologists call this the entity theory of intelligence, which is simply the belief that ability is innate and unchangeable. The more effective alternative, the incremental or growth-oriented view, treats intelligence as something that can be built through effort and strategy.

One of the most striking demonstrations of this comes from Blackwell and colleagues, who taught middle-school students that intelligence could grow like a muscle. Over the course of the year, those students steadily improved their math scores, while peers who held to the entity mindset flatlined. The same brains were faced with the same curriculum; the only difference was how those brains “spoke” to themselves about their own potential.

It’s fascinating that the internal script we run can literally change the trajectory of our performance. This makes it all the more sadder that so many of us still behave as if our mental ceiling is fixed, even though the door to improvement stands wide open, and we don’t even notice it.

2. We deprive our brains of the sleep they need.

Decades of research show that sleep is far more than simple downtime or a nightly round of shepherding virtual sheep. It carries deep evolutionary weight, appearing even in some of the simplest known lifeforms, such as the upside-down jellyfish (Cassiopea), which sleeps despite having no brain at all.

For us, sleep is when the brain rehearses, repairs, and rewires what it has learned during the day. Skip it, and you degrade performance in measurable ways where our executive function dulls and our decision-making falters.

In one EEG study, Zing et al. found that 24 hours of sleep deprivation significantly increased latency and reaction time, a clear marker of cognitive drag. Other research shows that even modest nightly sleep restriction impairs attention, working memory, mood, and judgment.

It’s no surprise, then, that sleep is integral to the well-being of so many species. Our brains are wired to the rhythms of an internal clock, and we’d be far better off if we lived more closely by it.

3. We drink alcohol.

Alcohol is perhaps the most obvious form of self-sabotage.

Anyone who’s had more than a glass of wine knows how thinking changes under the influence, but the damage can reach far deeper than we expect.

Recent findings by Justo et al show that consuming eight or more alcoholic drinks per week is linked to clear markers of brain injury. In a large autopsy-based study of 1,781 individuals, heavy drinkers had 133 percent higher odds of vascular brain lesions such as hyaline arteriolosclerosis; even former heavy drinkers were 89 percent more likely to have these lesions compared to non-drinkers. Tau tangles, hallmarks of Alzheimer’s disease, were 41 percent more common in heavy drinkers and 31 percent more common in former heavy drinkers.

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As such, it seems that even moderate drinking can exact a long-term toll on your cognitive edge. If you care about mental clarity and longevity, cutting back, or at least weighing what you trade for the buzz, may be one of the smartest choices you make.

4. We don't give our brains structure.

Our brains thrive on structure, purpose, and deadlines. Without them, we drift unfocused, sabotaging any spark of creativity we hoped to ignite.

A 2021 study by Rinaldi and colleagues found that undergraduates who reported higher levels of procrastination also showed measurable impairments in executive functioning, using established neuropsychological tests to back it up. That finding hits hard on all of us who suffer from procrastination, and it hints at how even the most brilliant thinkers need disciplined structure to function at full capacity.

Blank canvases may inspire, but relentless execution demands momentum and deadlines. Leave open lines to pick up tomorrow and build continuity so your brain wakes already mid-stride instead of staring into the void.

5. We put our brain in bad company.

Finally, we sometimes leave our brains in the worst possible company.

It’s the mental equivalent of leaving candy on your desk when you’re on a diet: You might resist for a while, but eventually your guard slips. The same thing happens with the mind. Place it in a steady drip of bad inputs, gossip, outrage, and low-grade distraction, and it will inevitably adapt downward.

Context matters greatly to what our brains end up getting up to. For example, studies in developmental psychology show that even emotions can spread among networks. In one longitudinal analysis, teenage moods became more similar over time to those of their peer group, and it was negative mood that proved especially contagious (Eyre, House, Hill, & Griffiths, 2017). In other words, your mental baseline quietly shifts to match the emotional “diet” you’re fed.

What Do Many Bad Brain Habits Have in Common?

Zoom out and you'll see that all five of these traps share a similar root cause: They thrive in the absence of self-awareness. Without noticing what’s going on in our own minds, we're doomed to run these patterns on autopilot without end. And while awareness alone won’t solve the problem, it is the only place we can begin.

Once we’ve named the habits that dull our edge, the real work begins. Whether that’s protecting sleep, curating the company we keep, setting deadlines, or changing the way we talk to ourselves about our own intelligence, each is a powerful tool for steering the brain toward its best work.