I don't think that when we were born defines who we are, but at the same time, it is rather eerie when you read the profile of your zodiac (either sun sign or Chinese) and it aligns so well with your personality.
If you throw enough darts you're bound to hit a bullseye. I'm a Sagittarius, let's see what it has to say about me.
"Spirit moving beyond the realm of the individual into the world at large; becoming a member of a wider society; experiences that lead to consciousness expansion, being receptive to new points of view, wisdom, enlightenment; using your talents for the benefit of the greater whole.
Freedom loving, idealist, unfettered by "small thinking"; inspiration; religion, philosophy, the law; awareness of your connections to the rest of the world; can be distant from others, afraid to give up freedom, reluctant to be tied down; on the other hand, aware of the value of the social contract; enthusiastic, gregarious, generous; loves abstract, theoretical ideas, sees the big picture, ignores the details; in love with an ideal; foreign travel, liberating experiences. "
First sentence: WTF? Second sentence: well this applies to everyone except the most serious recluses. Third: WTF? Fourth: everybody likes to think they are but they usually aren't, but will agree when told they are. Fifth: again, people like to think they have talents and that they help people, but rarely are both true. We like to be told that, though.
The next paragraph shows all the usual astrology tools. It throws out a lot of qualities so at least a few will seem "spot on." It uses flattery. "reluctant to be tied down; on the other hand, aware of the value of the social contract." There it throws out two opposing qualities. Everyone feels one sometimes and the other sometimes, so it fits every reader.
I read descriptions for other signs and they "fit" just as well.
Additionally, most people aren't even the sign that they think they are since the vernal equinox has shifted in the last few thousand years. Oddly I am still a Sag, though I went from the very end to the very beginning.