Psychologist Bertram Forer gave 39 of his students a personality test. Each was given a personalised profile based on their answers.
Except they were all given the same profile…taken from an astrology book.
When asked to assess how well it described them, on a 0-5 scale, the students reported an average of 4.3.
Wikipedia describes the Forer effect as
…a common psychological phenomenon whereby individuals give high accuracy ratings to descriptions of their personality that supposedly are tailored specifically to them, yet which are in fact vague and general enough to apply to a wide range of people. This effect can provide a partial explanation for the widespread acceptance of some paranormal beliefs and practices, such as astrology, fortune telling, aura reading, and some types of personality tests.