Personality Theory and Why It Matters for Investors - Behavioral Finance Chapter 4
Chapter 4 of Behavioral Finance and Investor Types by Michael M. Pompian takes a step back from finance entirely. Instead, it walks through the history of personality theory. Why? Because before you can classify investor types, you need to understand how psychologists figured out personality types in the first place.
Fair warning: this chapter reads more like a psychology textbook than a finance book. But it sets up everything that comes later.
It Started with the Ancient Greeks
Pompian traces personality theory all the way back to Hippocrates around 400 B.C. The idea was simple. People fall into four categories based on bodily fluids (yes, really): Melancholic, Sanguine, Choleric, and Phlegmatic. Today we’d call these Guardians, Artisans, Idealists, and Rationalists.
Plato had his own version too. He split the soul into three parts: appetitive (basic desires), rational (thinking), and spirited (the part that dishes out guilt or pride). Sound familiar? It should. Freud basically recycled this idea 2,300 years later.
Four Modern Schools of Thought
The chapter covers four major personality theories. Here’s the quick version.
1. Trait Theory (Cattell and Eysenck)
Trait theorists use data and statistics to isolate personality traits. Raymond Cattell built a hierarchy of traits, from broad ones like introversion-extraversion down to very specific ones. He even had a formula: your behavior is a function of the situation you’re in multiplied by your personality.
Hans Eysenck proposed three dimensions: extraversion-introversion, neuroticism, and psychoticism. His most interesting contribution was connecting introversion to actual brain biology. Introverts have a more sensitive nervous system that gets stimulated easily without much external input. Extraverts need more outside stimulation to feel engaged. It’s not just preference. It’s wiring.
2. Behavioral Theory (Skinner and Bandura)
Behaviorists don’t care much about what’s going on inside your head. They focus on what you do and how your environment shapes it.
B.F. Skinner is the Pavlov’s dog guy. Well, sort of. Pavlov did classical conditioning (ring a bell, dog salivates). Skinner flipped it around with operant conditioning. Put a pigeon in a box with a disk. Pigeon pecks randomly. Eventually it hits the disk and gets food. Soon the pigeon only pecks the disk. Behavior shaped by consequences.
Here’s the thing. Pompian admits he had the same reaction you’re probably having: what does this have to do with personality? The answer is that Skinner’s ideas apply outside the lab. We reinforce behaviors in each other all the time without realizing it. Smile politely at someone who won’t stop talking, and you just trained them to keep talking. Our environment shapes us, and we shape our environment right back.
Albert Bandura added something important. We don’t just learn from our own rewards and punishments. We learn by watching other people. You see a coworker work extra hours and get promoted, you start working extra hours. No one trained you. You just observed and adjusted. Bandura called this social cognitive theory, and it’s a big deal for understanding why investors copy each other’s behavior.
3. Humanist Theory (Rogers and Maslow)
The humanists were basically the optimists of psychology. While Freud focused on what goes wrong with people, Rogers and Maslow focused on what goes right. Their big idea is self-actualization: the drive to realize your full potential, whatever that looks like for you.
Maslow built his famous hierarchy of needs. You’ve probably seen the pyramid. Physiological needs at the bottom (food, water), then safety, then love and belonging, then esteem, and self-actualization at the top. You can’t worry about higher-level stuff until the basics are covered. You’re not contemplating your life’s purpose if you haven’t eaten in three days.
Rogers added the concept of unconditional positive regard. To become your best self, you need people around you who accept you without judgment. And you need to accept yourself the same way.
4. Psychodynamic Theory (Freud and Jung)
This is the big one. Freud believed personality comes from the tension between our basic instincts and our attempts to control them. He split the mind into three parts:
- Id: the part you’re born with. Pure impulse. No morality, no logic. Think of a newborn. Wants what it wants, doesn’t care about consequences.
- Ego: develops around 6-8 months. The reality check. It figures out which impulses are safe to act on and which will get you in trouble.
- Superego: your conscience. Shows up around age 3-5. It rewards you with pride when you behave and punishes you with guilt when you don’t.
Freud also believed your personality is basically set by age six. That’s debatable, but the id-ego-superego model is useful for understanding why investors do irrational things. Sometimes the id just wins.
Carl Jung was Freud’s colleague but disagreed with him on plenty. Jung’s big contribution was his personality typology. He proposed two attitudes (introversion vs. extraversion) and four functions (thinking, feeling, sensation, intuition). Combine them and you get eight personality types. If this sounds like the basis for Myers-Briggs, that’s because it is.
Jung also believed in the principle of opposites. Your personality has contradictions, and these contradictions create psychic energy. An introvert might become more extraverted over time as the psyche tries to balance itself out. He called this enantiodromia, which is a fancy word for “things eventually swing the other way.”
Why Any of This Matters for Investing
Pompian is upfront that personality science isn’t exact. People are complicated. But here’s the point: if you want to build a framework for understanding investor behavior, you need to stand on the shoulders of the people who spent decades studying human personality. Trait theory, behavioral theory, humanist theory, psychodynamic theory. Each one explains a piece of why we do what we do.
The next chapters will get into personality testing and eventually the Behavioral Investor Types framework. But this chapter lays the groundwork. Your investment decisions aren’t just about numbers. They’re about who you are. And understanding who you are starts with understanding how psychologists have thought about personality for the last 2,400 years.
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