Joachim Andersen

Accelerated Learning

Herd Mentality: Why We Follow the Crowd

A tight cluster of small antique brass sheep figurines walking the same way across a dark walnut table at night, with one brass sheep standing apart and facing the opposite direction
The crowd is a source of information, not a substitute for judgment.


Herd Mentality is the tendency to adopt the beliefs and behavior of a group because other people are doing it, rather than because I have weighed the evidence myself. When I am unsure what to do, the crowd offers a quick answer, and following it feels both safe and sensible.

Often it is sensible. If a whole room suddenly heads for the exit, I would be wise to follow before asking why. But the same instinct also makes us queue for the restaurant with the longest line, adopt the tool everyone at work is talking about, or hold an opinion simply because it seems to be the one everyone around us holds.

The essence of Herd Mentality is to ask: “Would I still choose this if I could not see what everyone else is doing?”


Origin: Instincts of the Herd

In the late 19th century, the social psychologists Gabriel Tarde and Gustave Le Bon described the “group mind” and the behavior of crowds. In 1916, the surgeon Wilfred Trotter published Instincts of the Herd in Peace and War, arguing that humans, like other social animals, are deeply sensitive to the opinions and actions of their group, and that this shapes even beliefs we think we have reasoned our way to.

In 1992, economists gave the idea a surprising twist. Abhijit Banerjee, and separately Sushil Bikhchandani, David Hirshleifer and Ivo Welch, showed that herding can happen even when every person acts rationally. If I see others choosing something, it’s reasonable to assume they know something I don’t. But once enough people follow those before them, everyone stops using their own information, and the whole group can confidently march in the wrong direction.


Key Concepts

  • Social Proof
    When we’re uncertain, we treat what others do as evidence of what is right, as I describe in The Psychology of Persuasion.

  • Information Cascades
    When people copy the choices of those before them instead of using their own knowledge, a crowd can grow large without containing much information at all.

  • Conformity Pressure
    Sometimes we go along not because we believe the group is right, but because we don’t want to stand out or be wrong alone.

  • Reputational Herding
    As the economist John Maynard Keynes put it, “worldly wisdom teaches that it’s better for reputation to fail conventionally, than to succeed unconventionally”.

  • Independence Matters
    A crowd can be wise when people judge independently, but its wisdom disappears when everyone is copying everyone else.


Some Examples

  • The Crowd That Looked Up
    On two winter afternoons in 1968, Stanley Milgram, Leonard Bickman and Lawrence Berkowitz placed groups of people on a busy New York sidewalk and had them stop and stare up at a sixth-floor window for 60 seconds. They filmed 1,424 passersby. When a single person looked up, 4% of passersby stopped beside him and 42% looked up as well. When the crowd was 15 people, 40% stopped and 86% looked up. There was nothing to see.

  • The Lines That Were Obviously Different
    In the 1950s, Solomon Asch asked students to say which of three lines matched a reference line in length, a task almost nobody got wrong alone. But when the other people in the room, who were actors, all gave the same wrong answer, about one-third of the answers on those trials followed the group, and 74% of participants conformed at least once. When just one other person gave the correct answer, conformity dropped sharply.

  • The Hit Songs That Could Have Been Different
    In 2006, Matthew Salganik, Peter Dodds and Duncan Watts created an online music market where 14,341 participants could listen to and download 48 songs by unknown bands. Some participants saw only the song titles, while others were split into eight separate worlds where they could also see how many times each song had been downloaded. Seeing the download counts made success more unequal and less predictable. The best songs rarely did poorly and the worst rarely did well, but almost anything else could happen, and the same song could be a hit in one world and ignored in another.

  • The Tool Everyone Was Adopting
    At work, I can feel the pull to adopt a new tool or method because it seemed that everyone else was. When I asked the people I was following why they had chosen it, several told me they had chosen it because others had. The popularity was real, but much of the evidence behind it was borrowed.


Applying Herd Mentality

I don’t want to ignore the crowd, because other people often know things I don’t. What I want is to know whether I am following information or just following. This is the simple process I use:

  1. Decide Privately First
    Before I look at reviews, rankings or what colleagues think, I write down my own view, so that I know what I thought before the crowd told me.

  2. Ask What the Crowd Knows
    I ask whether the people I am following have information of their own, or whether they are copying those ahead of them, as in an information cascade.

  3. Look for Independent Judgments
    I give more weight to opinions that were formed separately than to many opinions that came from the same source.

  4. Be or Find the First Dissenter
    Asch’s studies show that a single ally makes it much easier to speak up, so I try to be that person for others, and I invite dissent before a group settles on an answer.

  5. Watch for Excitement Without Reasons
    When something spreads quickly and people can describe its popularity better than its merits, I slow down, as I describe in The Psychology of Social Contagion.


Pitfalls and Limitations

  • Following the crowd is often rational. Other people’s choices contain real information, and ignoring them completely would make me worse at many decisions, not better.

  • Contrarianism, for it’s own sake, is not independence. Doing the opposite of the crowd by reflex is still letting the crowd decide for me.

  • The effect varies. In 1996, Rod Bond and Peter Smith reviewed 133 studies using Asch’s line task in 17 countries and found that conformity in the United States had declined since the 1950s, and that it tended to be higher in more collectivist cultures.

  • Markets may still be hard to beat. Herding can push prices too far, but that does not mean I can reliably tell when, as I describe in The Efficient-Market Hypothesis.


Related Mental Models

Herd Mentality reminds me that a crowd can be a source of information or simply an echo. By forming my own view first, asking what the crowd actually knows and valuing independent judgments over popular ones, I can learn from others without letting them think for me.



To learn more about mental models and philosophy,
check out: Wise: How to Attain a Deep Understanding of the World, History, Our Place in It, and How to Live Well



📚 Sources and References