Three points to consider.
Firstly, I can see that there can be a very slight correlation between birth signs and character. Not much more than a Spring/Summer/Autumn/Winter connection though, and probably less so now, than when we were living in caves. Being a Spring child, one would have had a less stressful first six months than an Autumn child, who had to survive the Winter when tiny. Of course, this correlation would be reversed in the southern hemisphere.
Secondly, as so many people do take notice of their star signs, I suspect that they suffer from auto-suggestion, and become the character they are told they should be.
Finally, coincidences happen. I'd be extremely worried if they didn't, as that would show that someone was preventing them from happening.
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"Striking up conversations with strangers is an autistic person's version of extreme sports."
Kamran Nazeer