Person x Situation = Behavior

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Most of us are used to thinking of people in terms of their personality traits: “David’s a pretty quiet guy.” “Mia’s a bit of a drama queen.” “Adrien is a naturally bubbly person.”

We tend to imagine that these personality traits—characteristic patterns of thought, feelings, and behavior—are pretty stable and consistent. And for many years, psychologists believed the same.

In the 1920s, when early personality psychologists began theorizing about the differences between introverts and extroverts, they imagined that these traits would be fairly stable across time. And they supposed that personality was a reasonable causal explanation of behavior: on a certain occasion if a person talked a lot, it was presumably because he or she was an extroverted person.

But in 1968, a psychologist named Walter Mischel issued a challenge to that paradigm, arguing that people are in fact highly inconsistent, with behavior that varies wildly from one situation to the next. Because behavior is not cross-situationally consistent, Mischel argued, theories of personality were predictively worthless. Because the same person acts differently in different situations, what matters is not personality but the influence of the situation.

Several experiments from that era highlighted the power of the situation to influence behavior. Most notable of these was Stanley Milgram’s classic study on obedience to authority[1].

Milgram’s study found that when confronted with an order from a perceived authority figure (the “experimenter” in the study), a high proportion of research subjects were willing to administer what they believed was a painful or even fatal electrical shock to a study participant in the next room (actually a trained actor). Given a certain set of circumstances, it seemed, ordinary people were capable of extraordinary evil. The conclusion seemed inescapable: situations, not personalities, determine behavior.

A resolution to the person vs. situation debate came in 1979 when Seymour Epstein found that there actually are stable differences between people—if you aggregate behavior across multiple situations[2]. Yes, people do behave differently in different situations, but there are also stable differences between individuals in their average levels of behavior. In other words, both approaches are correct.

Today, psychologists agree that personality factors and situations both contribute to behavior: Personality x Situation = Behavior. Studies suggest that situational variables are more relevant in predicting behavior in a given situation, whereas personality traits are more useful for understanding patterns of behaviors over time[3].

As it turns out, we’re all also prone to a mental bias that affects how we reason about personality and situations. When we think about our own behavior, we’re aware of the influence of the situation (“I snapped at the Über driver because I’ve been running around all morning and haven’t even had breakfast”). But when we’re judging other people, we attribute their behavior to personality factors (“That guy is a jerk”)[4].

In reality, everyone’s behavior is the result of a complex interaction between personality and situational variables. As psychologist Scott Barry Kaufman puts it:

I think we tend to overplay our differences, and underestimate just how similar we all really are deep down in our basic needs, strivings, and frustrations. Our common humanity. Emerging research shows that even though we each show distinct patterns of thoughts, motivations, and behaviors that make us different from each other, we actually display the whole spectrum of behaviors in our everyday life. Everybody sometimes gets tired from too many social interactions, sometimes acts like a jerk, sometimes is lazy, etc. Just some of us are consistently more so on a regular basis than others[5].


1. Milgram, S. (1974). Obedience to authority: An experimental view. New York: Harper & Row.
2. Epstein, S. (1979). The stability of behavior: I. On predicting most of the people much of the time. Journal of Personality and Social Psychology, 37, 1097-1126.
3. Fleeson, W., & Noftle, E. E. (2009). The end of the person-situation debate: an emerging synthesis in the answer to the consistency question. Social and Personality Psychology Compass, 2, 1667-1684.
4. Ross, L. (1977). The intuitive psychologist and his shortcomings: Distortions in the attribution process. Advances in Experimental Social Psychology, 10, 173–220.
5. Kaufman, S.B. (2016). Both introverts and extraverts get exhausted from too much socializing. Scientific American.