The Barnum Effect (also known as the Forer effect) is named for the following expression attributed to the 19th century showman P.T. Barnum: We have something for everyone. Study of this effect, or phenomenon, shows that people identify with and easily accept information that is favorable to them and/or their personal belief system.
This principle is the basis for the existence of newspaper astrology columns, phone psychics, fortune cookie predictions, etc...
The individuals who practice these types of industries and activities are well versed in the means of communicating information that is both positive and non-specific and is designed to speak to people's hopes, dreams and expectations.