What Causes Aggression? The Psychology of Why We Hurt Others

Aggression can take many different forms. It can show up in the way we roll our eyes, snap at someone in a meeting, or send a pointed email. It’s not always loud, but it’s always felt by those on the receiving end.

So what causes aggressive behavior? And more importantly, what can we do about it?

In this post, we’ll explore the psychology of aggression: where it comes from, how it shows up, and what factors make it more likely to appear. We’ll look at classic studies that explain why ordinary people can act in harmful ways, and we’ll share practical strategies to recognize and regulate aggressive impulses before they cause damage.

What Is Aggression?

At its core, aggression is behavior intended to harm someone, physically, emotionally, or psychologically. That intent is key. It’s not just about anger; it’s about acting on that anger in a way that hurts another person.

Aggression can take many forms, but psychologists generally divide it into two types:

Hostile aggression (emotion-driven)

This is the type of aggression that bubbles up when you’re angry. It’s impulsive, hot-headed, and emotional. You want the other person to feel what you’re feeling, usually hurt or shame.

• Example: You feel insulted in a meeting, so you throw a passive-aggressive jab or storm off.

Instrumental aggression (goal-driven)

This one is more calculated. The goal isn’t emotional release, it’s achieving something, even if it means someone else gets hurt along the way.

• Example: You sabotage a coworker’s project to get ahead. You’re not angry, you just want the promotion.

Both types can be harmful. One is emotional; the other strategic. But they share the same root: harming others to meet some internal need.

What Triggers Aggression?

Aggression can be triggered by internal stress, external conflict, or a mix of both. Once we understand what sets it off, we can start to manage it better.

Frustration and blocked goals (Frustration-Aggression Theory)

When something (or someone) gets in the way of something important to us, we get frustrated. If that frustration lingers or feels unfair, it often turns into aggression.

Think: You’ve worked hard on a proposal, and your manager shuts it down with no explanation. Your frustration builds, and suddenly you find yourself talking negatively about them to others. That’s aggression fueled by blocked progress.

Insecure or low self-esteem

People with shaky self-worth often react aggressively to perceived slights or criticism. It’s a defense mechanism –lash out before anyone sees the vulnerability.

Interestingly, it’s not always low self-esteem that leads to aggression. Sometimes it’s unstable or inflated self-esteem that cracks under pressure.

Social and group dynamics (dehumanization, conformity, diffusion of responsibility)

We behave differently in groups. And not always for the better. Psychologists like Philip Zimbardo and Albert Bandura have shown how ordinary people can commit harmful acts when:

• They feel anonymous

• They believe others are responsible

• They’re following group norms

• They see the other person as "less than"

Aggression becomes easier when empathy is low and peer pressure is high.

Poor early socialization (hostile environments)

How we’re raised matters. People who grow up in emotionally cold, punitive, or aggressive homes are more likely to develop aggressive patterns themselves.

These early environments shape:

• How we handle frustration

• How we see others

• Whether we view the world as a safe or hostile place

The Psychology of Aggression

So what’s happening beneath the surface?

Evolutionary roots

From an evolutionary perspective, aggression had its place. It helped our ancestors compete for resources, defend themselves, and assert dominance in social hierarchies.

But what was once a survival mechanism can easily become destructive in modern life.

Neuropsychobiology

Certain brain structures and chemicals are involved in aggression:

• Amygdala: linked to fear and emotional reactivity.

• Prefrontal cortex: helps regulate impulses (when it’s underactive, control weakens).

• Testosterone & cortisol: hormonal influences on aggressive tendencies.

When the balance is off, either from stress, sleep deprivation, or trauma, aggression becomes more likely.

The role of perception and bias

We don’t just react to reality. We react to our perception of reality.

If we feel threatened, ignored, or disrespected (even if that wasn’t the other person’s intention), our brains may flip into a defensive, aggressive mode. This is especially true when we’re tired, overwhelmed, or operating on autopilot.

Real-World Examples of Aggression in Action

Aggression isn’t always obvious. Sometimes it’s a whisper instead of a roar.

Zimbardo's Stanford Prison Experiment

Philip Zimbardo's famous study placed ordinary college students into the roles of guards and prisoners in a simulated prison environment. The results were startling. Within just a few days, the "guards" began exhibiting cruel and authoritarian behaviors, while the "prisoners" became passive and distressed. The experiment was cut short after only six days due to the psychological harm being done.

Conclusion: When given power and anonymity within a system that encourages dominance, people can adopt aggressive behaviors that go against their own morals. The situation, not the person, often shapes behavior.

Milgram's Obedience Study

Stanley Milgram wanted to understand how far people would go in obeying authority, even when it meant harming another person. Participants were instructed to deliver electric shocks to a stranger (actually an actor) when they gave wrong answers to questions. Shockingly, over 65% of participants continued to deliver increasingly severe shocks simply because they were told to.

Conclusion: People are capable of harmful actions when they feel the responsibility lies with someone else. Authority figures can heavily influence moral decision-making.

Bandura's Work on Dehumanization

Albert Bandura explored how people justify aggressive behavior by dehumanizing their victims. In one study, participants who heard their target referred to as an "animal" or "criminal" were more likely to administer painful actions. Once empathy is stripped away, aggression feels more permissible.

Conclusion: Language and labeling matter. When we view others as less human, it becomes easier to act without empathy.

Together, these studies show how social and group dynamics, especially anonymity, conformity, and dehumanization, can dramatically increase the likelihood of aggression.

Lesson? The right (or wrong) environment can make almost anyone aggressive.

Workplace scenarios

A manager consistently micromanages and criticizes a team member, not out of malice, but out of insecurity. A colleague excludes someone from meetings or emails as a way to assert dominance. Passive-aggressive comments or eye rolls in a team setting.

All of these are forms of aggression, even if they never make headlines.

How to Regulate Aggressive Behavior

Aggression isn’t something you "have or don’t have." It’s something you can understand, track, and regulate.

Build emotional self-awareness

Most aggressive reactions start before we even notice them.

• Name your triggers: What tends to set you off?

• Track your signs: Does your heart race? Do you feel hot? Do you go quiet before you snap?

• Build a pause: Take a breath, label the feeling, and ask: "What’s really happening here?"

Improve coping strategies

We all need ways to release tension. Without them, aggression finds its own outlet.

• Move your body

• Talk it out

• Journal

• Get curious instead of reactive

You can’t always control the trigger, but you can control your response.

Create more connected environments

Aggression thrives in isolation and disconnection.

Empathy, feedback, and human connection act as buffers. When we see each other as people, not objects or obstacles, we're far less likely to lash out.

Try this:

• Use people’s names

• Ask for their perspective

• Assume good intent (until proven otherwise)

• Encourage self-reflection over blind obedience

Whether in companies or families, people follow what they’re taught.

Question harmful group norms

Speak up against "just following orders"

Promote ethical decision-making, not just rule-following

What’s Your Default Response Under Stress?

Aggression isn’t about being a bad person. It’s often about being a stressed, hurt, or overwhelmed person without the tools to respond differently.

When was the last time you:

• Reacted sharply and regretted it later?

• Withdrew instead of explaining how you felt?

• Said something to hurt someone before they could hurt you?

I’ve never seen myself as an aggressive person. But the more I understand what causes aggression in others and how it can build up under the surface, the easier it is to navigate difficult moments with a bit more compassion and a lot less defensiveness.

Not in a way that excuses bad behavior, but in a way that helps me stay grounded in my own response, even when someone else loses theirs.

"Your mind is not always your friend. But it is always your responsibility." –Matt Haig

References

• Bandura, A., Ross, D., & Ross, S. A. (1961). Transmission of aggression through imitation of aggressive models. The Journal of Abnormal and Social Psychology, 63(3), 575–582. https://doi.org/10.1037/h0045925

• Baumeister, R. F., Campbell, J. D., Krueger, J. I., & Vohs, K. D. (2003). Does High Self-Esteem Cause Better Performance, Interpersonal Success, Happiness, or Healthier Lifestyles?. Psychological science in the public interest : a journal of the American Psychological Society, 4(1), 1–44. https://doi.org/10.1111/1529-1006.01431

• Dollard, J., Miller, N. E., Doob, L. W., Mowrer, O. H., & Sears, R. R. (1939). Frustration and aggression. Yale University Press. https://doi.org/10.1037/10022-000

• McDermott, R. (2007). The Lucifer Effect: Understanding How Good People Turn Evil – By Philip Zimbardo. Political Psychology, 28(5), 644–646. https://doi.org/10.1111/j.1467-9221.2007.00597.x

• Reeve, J. (2018). Understanding motivation and emotion (7th ed., Chapters 3 and 4). Wiley.

• Simó, S. (2025). Psychology of motivation and emotion [Lecture notes]. Facultat de Psicologia, Universitat de València.