I know a few who do not fit the description of the sign they are. For some people, before I know their birthdays, if they do something or make some comment I will say something like "gosh, you are such a scorpio (or whatever I think they are)." Usually I am right, but sometimes I am wrong, and I actually kind of baffled! Is it just me or are there others who know what I am talking about?
I never used to match my sign. I'm a Capricorn but all my other signs (except for moon in Taurus) are air or water. So bascially, I'm a walking contradiction of ambition and logic in some situations, and affection and emotion in others. I've grown more into my Capricorn-ness.
What's there to be confused about? You have a Sun sign and then you have planetary influences - so let's say that this person has 10 planets in one sign. This person will be completely different than a person that has 10 planets equally spaced throughout. But mostly they're different because of their upbringing and environment, through Fate and circumstance. Existence has made everyone unique. There has never been nor will there ever be another person exactly like you or me. It is therefore best to use astrology to understand oneself but not anyone else.
There are billions of personalities, but there are a lot of characteristics that people have that makes me be able to distinguish what sign they are. Like people who are really vein are often leos or scorpios, neat and very orderly people are virgos often, blah blah---maybe it just makes more sense in my mind.