What does the Wiccan Rede really mean to you?

The Rede says, "And it harm none, do what you will." Technically speaking, what this is saying is that "If it harms none, then it is permissible." Logically, taken from just that, something could still be permissible even if it harmed someone. For example, I could say "If my sister is a university student, then she is a human being." BUT, she doesn't*have* to be a university student to be human. So the reverse doesn't follow from that -- it is false from the first statement that if my sister is not a university student, then she is not a human being. Similarly, "If it harms none, then it is permissible" just does*NOT* imply the opposite, that "If it harms someone, then it is impermissible." That's a mistake in reasoning. So when are things impermissible? Do you disagree with this meaning of the Rede? Thoughts in general? :)