It's biologically ingrained:
The tendency to believe vague statements designed to appeal to just about anyone is called the Forer Effect, and psychologists point to this phenomenon to explain why people fall for pseudoscience like biorhythms, iridology and phrenology or mysticism like astrology, numerology and tarot cards.
The Forer Effect is part of larger phenomenon psychologists refer to as subjective validation, which is a fancy way of saying you are far more vulnerable to suggestion when the subject of the conversation is you.
2006-2011 archives for The Daily Dish, featuring Andrew Sullivan