I once read about a demonstration that was done in a class (college or high school, I don't remember which).  Every student provided a bunch of information about when and where they were born.  Later on, every student was given a piece of paper in a sealed envelope.  They were told that the piece of paper was a detailed horoscope that a professional astrologer had written for them personally based on the exact information they provided.

After reading the horoscopes, the students were asked to rate the accuracy from 1 to 5, with 5 being the most accurate.  All students rated it either 4 or 5.  Then, they traded horoscopes with another student and read the other student's horoscope.

It turned out every student had received the same horoscope, and every student had believed that it was accurate for them.

Take from this what you will.  ;)

Because I love science, I did a little experiment. I asked several friends what their signs were. Then I read the characteristics from any of the other signs and they said "yes, that's me exactly" or "yes, some of the things are true", but no one said that all of the characteristics were not true. The results reflect what Jacob said "... exist in everyone's personalities". Good topic Jacob.

Wellcome to the club, I'm Gemini too, and it's really disturb me sometes

I belive and follow it. 

I think the characters which are described in different signs all exist in everyone's personalities, we believe in signs because they notice us some aspects of our own personalies, and then we'll focus on those aspects and feel the signs do make sense.

My sign is Gemini. So I am a capricious person? Hahah, maybe, even though I don't wanna admit it.