What is the Horn Effect Bias?

The horn effect, coined by Thorndike (1920), often called the forked-tail effect, is a cognitive bias (a form of confirmation bias) that causes one’s perception of another person to be unduly influenced by a single negative trait.

More specifically, the Horn effect is the tendency to cause an individual’s perception of another to be influenced dramatically by negative aspects of that individual.

It is the opposite of the Halo Effect.

We tend to make negative judgements and assumptions about individuals by attributing it to a specific negative aspect of their trait, personality or appearance.