Bill reminded Susan that he wanted to meet her friend. Now check it out without the pronouns. Bill reminded Susan that Bill wanted to meet Susan's friend. This second construction is awkward and confusing. Luckily, we have the pronouns he and her.
Grammarians call pronouns that substitute for beings and objects, personal pronouns.
He earned the poetic license by knowing the rules of grammar and punctuation before he broke them. Understanding how pronouns function can help a writer resolve some tricky grammatical situations. Pronouns and their antecedents must agree in number, gender, and person. I like hot peppers even though they give me heartburn. Either that, or some poor guy is named Susan.