The Forer Effect

Aka known as The Barnum Effect:

The Forer effect (also called personal validation fallacy or the Barnum effect after P. T. Barnum’s observation that ‘we’ve got something for everyone’) is the observation that individuals will give high accuracy ratings to descriptions of their personality that supposedly are tailored specifically for them, but are in fact vague and general enough to apply to a wide range of people. The Forer effect can provide a partial explanation for the widespread acceptance of some pseudosciences such as astrology and fortune telling, as well as many types of personality tests.

A related and more generic phenomenon effect is that of subjective validation (Marks, 2000, p. 41). Subjective validation occurs when two unrelated or even random events are perceived to be related because a belief, expectancy, or hypothesis demands a relationship. Thus people seek a correspondence between their perception of their personality and the contents of a horoscope.