Here's why:
* Subject pronouns (I, you, he, she, it, we, they) act as the subject of a verb. They tell us who or what is doing the action.
* Possessive pronouns (mine, yours, his, hers, its, ours, theirs) show ownership or possession. They tell us who or what something belongs to.
Example:
* Subject pronoun: He is reading a book. ("He" is the subject performing the action "reading").
* Possessive pronoun: This is his book. ("His" shows that the book belongs to him).