Do you know why our brains can replay our most embarrassing moments from years ago in high resolution, but struggle to remember a compliment from last week? The reason is our brains’ tendency to hold onto negative thoughts more tightly than positive ones, referred to as the negativity bias. And this cognitive bias is often amplified by another co-occurring phenomenon researchers call the negative sentiment override.

If you have experienced this too, you can take comfort in knowing that it’s not a unique personality quirk, but a phenomenon that’s been recorded and studied in evolutionary psychology for decades. This means that the mistake or past humiliation you keep reliving is, in all probability, really not that deep. This bias is a built-in feature of human wiring, shaped by evolution and reinforced by modern stress. And understanding why this happens can help you break the cycle and regain control of your mental narrative.

Here are the three main reasons your brain gravitates toward negativity and what you can do about it.

1. The Brain Evolved to Prioritize Negative Thoughts

Long before smartphones, deadlines or social media existed, humans had one job: to survive. And that meant paying extremely close attention to anything that could cause harm. A rustle in the bushes, subtle changes in weather and the strange pugmarks of a wild animal could all mean certain death if left unaddressed.

In other words, missing a potential threat could be fatal. Missing something positive, like a pretty tree or a pleasant sound, rarely had as severe a consequence.

Over thousands of years, this led the human brain to prioritize negative or threatening information. Even today, the brain uses the same ancient alarm system, treating social rejection, criticism, financial fears or uncertainty like potential threats to one’s survival.

Research also confirms that the amygdala, a critical brain structure for emotional processing, responds strongly to emotionally arousing stimuli. While it’s active for both positive and negative stimuli, evidence shows an especially strong prioritization when threat is perceived.

You might replay a coworker’s annoyed tone or a mistake you made, even though you’re physically safe in reality. In a moment like this, it’s important to remind yourself that your brain isn’t trying to torture you; it’s trying to protect you the best way it knows how.

2. Negative Thoughts Try to Prevent Negative Events

Psychological research has long documented the negativity bias: our tendency to remember negative experiences more vividly than positive ones. One eye-tracking study tested 130 undergraduate male students and found that people pay more attention to central details in negative emotional events, which makes these memories more deeply encoded.

This is because negative experiences activate more activity in the brain’s information-processing center, particularly the amygdala, which prioritizes emotionally charged memories. And it is this mechanism that might be playing out in the background when you:

• Forget five compliments but obsess over one critical comment
• Remember a mistake you made at work for years but struggle to recall a small daily accomplishment
• Replay embarrassing moments repeatedly and don’t revisit moments of pride with intention

Social psychologists have also found that humans assign more emotional weight to losses than to gains. This is known as loss aversion, and it shows up in everything we do, from how we interpret a drop in bank balance to how we react to criticism from loved ones.

This is the function our negativity bias evolved to perform. So, it doesn’t just shape memory; it changes decision-making, motivation and self-perception to prevent losses and other negative experiences in the future.

The problem is that unless you actively work to notice and reinforce positive experiences, your brain will continue defaulting to what’s wrong instead of what’s right, and this might lead to a permanently fear-based approach to life.

3. Negative Thoughts Create Emotional Feedback Loops

Once negative thoughts take hold, they trigger a stress response. Dwelling on negativity often leads to the release of cortisol, the stress hormone, which sensitizes your brain to more negative cues in turn.

This creates a powerful loop: a negative thought enters the brain, and, due to its distressing contents, the brain signals the body to activate its stress response. As a result, the brain and body become more sensitive to other negative information or stimuli, finally leading to even more negative thoughts accumulating in the brain.

A 2014 study published in *Psychoneuroendocrinology *found that post-stress rumination (replaying negative thoughts after a stressful event) predicted greater cortisol reactivity to future stressors. The brain adapts to expect danger (even when there isn’t any) and gives an even stronger response the next time it senses a potential threat. Rumination is one of the strongest predictors of anxiety and depression because it keeps the stress response activated.

Once these loops form, they can feel automatic. You might catch yourself thinking:

• “Why can’t I just let this go?”
• “Why do I keep thinking about this?”
• “Why does this bother me so much?”

But the brain is simply doing what it has been conditioned for years or even decades to do. The good news is that these loops can be disrupted with intentional mental habits, and the brain can reshape itself through repetition. Just as negative loops are formed, positive loops can also be built through intentional refocusing.

Negative thoughts cling to your mind because your brain is built to protect you, not to make you happy. But once you understand the survival mechanisms, psychological biases and emotional loops at play, you can begin to interrupt them. By slowing down, noticing your thoughts and intentionally nurturing positive experiences, you can train your brain to stop gripping negativity so tightly and start embracing the good with more ease.

A version of this post also appears on Forbes.com.