Why Do We Trust Our First Impression of Someone, Even When It’s Wrong?

Vocabulary

Thin-slicing – the mental process of making quick judgments about a person or situation based on a very small amount of information.

Example – Psychologists call snap judgments based on a few seconds of interaction “thin-slicing.”

Cognitive bias – a systematic pattern of thinking that can lead to inaccurate or irrational conclusions.

Example – Trusting a first impression too much can be a form of cognitive bias.

Evolutionary – relating to the gradual process by which living things develop and change over time.

Example – Some researchers believe quick judgments of strangers served an evolutionary purpose, helping early humans avoid danger.

Corroborate – to provide evidence that supports or confirms something.

Example – A single brief interaction is not always enough to corroborate a lasting judgment about someone’s character.

Discrepancy – a difference or disagreement between two things that are expected to be the same.

Example – Researchers found a surprising discrepancy between how confident people felt about a first impression and how accurate it actually was.

Article

It happens almost instantly. Someone walks into a room, says a few words, and within seconds we have already formed an opinion: trustworthy or suspicious, confident or nervous, competent or careless. What is remarkable is not just how quickly these judgments form, but how strongly we tend to trust them, sometimes even after we have gathered evidence that should change our minds.

The Science of “Thin-Slicing”

Psychologists have a name for this phenomenon: thin-slicing. The term, coined by psychologist Nalini Ambady, describes the brain’s ability to draw meaningful conclusions from an extremely brief slice of someone’s behavior, sometimes just a few seconds of observation. Research has found that five-second video clips of a person can produce judgments nearly as accurate as five-minute clips, and that people can reliably assess traits like sociability and competence in as little as six seconds.

This is not simply guessing. Thin-slicing research has demonstrated real accuracy across a surprising range of contexts, including judgments of trustworthiness, teacher effectiveness, and job performance. Many researchers believe this ability is evolutionary in origin, an adaptation that helped early humans rapidly assess whether a stranger represented a threat, an ally, or someone worth ignoring, long before language or extended social interaction was possible.

When Snap Judgments Get It Right

The accuracy of thin-slicing helps explain why we trust first impressions so deeply: often, they are not wrong. Studies have repeatedly shown that brief exposure to someone’s face, voice, and body language can accurately predict traits that would otherwise take much longer to confirm through conversation. In some experiments, judgments made from silent video clips, with no audio at all, still corroborated more detailed personality assessments made later.

This creates a kind of psychological shortcut. If quick judgments are frequently accurate, the brain has little incentive to slow down and second-guess them. Over an evolutionary timescale, trusting a fast read of another person was often more useful for survival than deliberating carefully, especially in situations where hesitation could be costly.

Where the System Breaks Down

The trouble is that thin-slicing is not equally reliable across every situation. Researchers have found that accuracy depends heavily on the type of judgment being made, how much exposure a person has to work with, and even the specific moment being observed. Someone caught on a bad day, distracted, anxious, or simply having an off moment, can produce a first impression that is confidently wrong rather than accurately right.

This creates a troubling discrepancy: people tend to feel just as confident about inaccurate first impressions as they do about accurate ones. Confidence and correctness are not the same thing, yet our brains rarely flag the difference in the moment. A cognitive bias toward trusting fast judgments means that even when new, contradicting information arrives later, people often unconsciously interpret it in ways that preserve their original impression rather than genuinely reconsidering it.

Certain traits are also far easier to judge accurately than others. Observable characteristics like extroversion or general likability tend to be assessed more reliably in a thin slice than deeper qualities like honesty, intelligence, or long-term reliability, which usually require sustained interaction to evaluate fairly. This means the traits people feel most confident judging quickly are not always the traits that matter most in high-stakes situations, like hiring decisions or forming close relationships.

The Real-World Stakes

This research carries serious implications well beyond casual social encounters. Hiring managers routinely make consequential judgments about candidates within the first few minutes of an interview, sometimes even before a single substantive question has been asked. Jurors, doctors, teachers, and interviewers are all vulnerable to the same rapid judgment process, and to the same risk of mistaking confidence for accuracy.

Recognizing this dynamic does not mean first impressions should be discarded altogether. Since they are often genuinely useful, the more productive lesson is learning to hold them a little more loosely: treating an initial read as a hypothesis rather than a verdict, and remaining genuinely open to evidence that might update or overturn it.

A Skill Worth Reexamining

Ultimately, the persistence of first impressions reveals something fundamental about how the human mind is wired: built for speed as much as for accuracy, and more comfortable defending an existing judgment than updating it. Understanding this tendency will not stop the brain from forming instant opinions. It cannot. But it can make people slightly more careful about how much weight they give those opinions once the evidence starts complicating the picture.

Discussion

Do you think your first impressions of people are usually accurate? Can you think of a time you were wrong?

Why do you think humans evolved the ability to judge strangers so quickly?

Do you think first impressions matter more in job interviews than they should?

Have you ever changed your opinion of someone significantly after getting to know them better?

Why do you think people stay confident in a first impression even after receiving evidence that contradicts it?

Which do you trust more: how someone looks and speaks, or what they actually say and do over time?

Should hiring processes be redesigned to reduce the influence of snap judgments? How?

Sources

APA (American Psychological Association): “Thin Slices” of Life

Psychology Today: Thin Slices & First Impressions

ScienceDirect: A Thin Slice Perspective on the Accuracy of First Impressions