A self-fulfilling prophecy is a prediction which causes itself to become true due to the positive feedback.
Another effect used in horoscopes is the Forer effect, also called the Barnum effect. It describes the situation when a person consider a description of his or her personality or character highly accurate, but this description is really vague and general and can be applied to a big number of people.
Background is commissioned by AlexSvar.
“The Barnum Effect in personality assessment: A review of the literature”, DH Dickson, IW Kelly, Psychological Reports, 1985.