Exactly, they are vague enough so that anyone can fit them to their situation and when they don't it doesn't matter, because in the long run there is always a huge amount of confirmation bias in those who believe.

Horoscopes have always had that effect for me too.  I don't believe in them, but they seem to always have those eerie moments when they're spot on.  Many are generally vague and apply to most people though, in my opinion.