The horn effect, also known as the reverse halo effect is a type of bias where someone’s initial negative judgement about someone influences their perceptions of them as a whole.

For example, a supervisor observed that a new employee spilt coffee on his first day and after that the supervisor thinks of him as clumsy. This type of incident does not happen again but the supervisor remembers this and gives him a mediocre review, even though his work has been outstanding.

The supervisor drew conclusions which were applied to a whole review based on this one negative impression.

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