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How the Brain Works

How the brain works according to Giovanni Ceroni: System 1 and System 2, the amygdala and prefrontal cortex, and why change is so exhausting.

You are not your mind. You're watching the output of a system that's running. And that changes the whole point of view.

What it is

The human brain, with its roughly 86 billion neurons organized into complex networks, is the system from which everything we call "mind" emerges: thoughts, decisions, interpretations. But in many ways its functioning is still "prehistoric": its primary job isn't to make us happy or to give us a better, healthier, more abundant, longer life, but simply to save energy.

Left untrained, the mental processes behind our decisions are structured mainly to achieve that energy saving. At the behavioral level, it does this through habits and routines, resisting sudden changes even when they're useful or necessary — this is why changing behavior is so exhausting. At the decision-making level, it looks for quick, cheap solutions, relying on heuristics and cognitive biases: mental shortcuts that let you reach quick conclusions, at the cost of lower accuracy.

Why it matters

Understanding this underlying mechanism matters because it explains, without moral judgment, why change is so often exhausting, and why the mind, when it thinks it's reasoning clearly, is often just following shortcuts that expose it to cognitive traps, hasty judgments and poor choices. This isn't a personal flaw, but the way the brain has learned to function over hundreds of thousands of years of evolution oriented toward survival, not wellbeing.

How it works

The brain uses two major decision-making systems. System 1 makes fast decisions, uses little energy, and doesn't trigger deep reasoning. System 2 makes elaborate, reflective, deliberate decisions, weighing the available options: it uses far more energy, and the brain doesn't like that — even though it can be trained through the right strategies and routines. The brain always favors System 1, because it better serves its primary goal of saving energy, regardless of the quality of the decisions made. Every time System 2 gets tired, decision-making gets rerouted to System 1: hence the importance of breaks and pauses during work that demands maximum attention.

The brain is, in a sense, "wired" to keep answering two questions: is this a threat? Is this an opportunity? The amygdala, the part of the brain that handles emotions, reacts instinctively to external events. It's the prefrontal cortex — home of rational decisions, estimated at about 16 billion neurons — that offers the power to consciously choose how to respond to those events, giving them the most useful meaning.

What we call emotion is, in this framework, a physiological process: chemistry, breathing, posture, the speed of thought and the quality of attention all shift. The brain can be compared to a "bartender" mixing different cocktails — adrenaline and cortisol when alertness is needed, serotonin, endorphins and oxytocin when pleasure, bonding or recovery is needed. Repeating a state several times doesn't make it "character": it simply makes it easier to reproduce. This is one of the foundations of experiential learning: what you train becomes more quickly accessible.

Common mistakes

A common mistake is considering your own decisions always rational and deliberate, without recognizing how often they actually come from System 1, especially when tired or stressed. A second mistake is expecting to keep System 2 constantly active for long periods, without planning breaks: System 2 gets tired, and when it does the brain automatically defaults to System 1. A third mistake is completely ignoring the physiological component of emotions, trying to manage them only at the level of thought, when in reality they involve chemistry, breathing and posture.

Practical example

During a long job interview, the hiring manager's System 2 tends to get tired as time passes. At that point System 1 takes over, focusing attention on likability, eloquence, clothing and appearance to quickly confirm the candidate's suitability, through confirmation bias: "they're personable, I like them, they look good." This often leads to bad hiring decisions. An effective fix is inserting lighter questions about hobbies or personal habits during the interview, alternated with skills questions: this gives System 2 time to rest, reduces decision fatigue, and has concretely reduced hiring mistakes.

Applications

Knowing how this works applies to managing selection interviews, designing work or study sessions that respect System 2's limits, managing stress and instinctive reactions in relationships, and more generally any situation where it's useful to recognize when you're deciding with real clarity and when you're simply following a mental shortcut.

Frequently asked questions

What are System 1 and System 2 of the brain?

System 1 is the one behind fast, automatic, low-energy decisions. System 2 is the one behind reflective, deliberate decisions, which requires far more energy — which is why the brain tends to avoid it when it can.

Why does the brain always favor System 1?

Because its primary goal isn't making the best decision, but saving energy. System 1 uses fewer resources, regardless of the quality of the outcome it produces.

Why is it so exhausting to change a behavior?

Because the brain, to save energy, resists sudden changes even when they're useful, relying on heuristics, mental shortcuts and biases to counter them.

What roles do the amygdala and the prefrontal cortex play?

The amygdala reacts instinctively to external events, handling the immediate emotional response. The prefrontal cortex is where rational decisions happen, and it lets you consciously choose how to respond instead of reacting automatically.

Why are breaks important during focused work?

Because System 2 gets tired with prolonged use, and when that happens the brain automatically shifts decisions over to System 1, which is faster but less accurate. Breaks let you "recharge" your capacity for deliberate reasoning.

Related concepts

What Are Heuristics, What Are Cognitive Biases, The Carriage Metaphor, What Is an Internal State, Concentration Techniques.

Go deeper

How the brain works, System 1 and System 2, are covered in the "Our Brain" chapter of Volume I of "The Invisible Blade", as a foundation for understanding the following chapter on heuristics and cognitive biases.

Giovanni Ceroni

Mental Coach and author of the La Lama Invisibile / The Invisible Blade series.