its not, read my story about zodiac signs:P its really cool!,
I don't really match my sign (Aries), I'm more like a Libra. they're accurate to a point, but there are always exceptions.
I match up with some of my Zodiac traits. One of my friends is of the same sign as I am, but we are completely different people. So in a nutshell, I don't think it's real.
It's not always about your sun :) Your other planets affect who you are as an individual too.