Here's why:
* Possessive pronouns show ownership. They indicate that something belongs to someone or something. Other possessive pronouns include: mine, yours, his, hers, ours, theirs.
* Subjective pronouns are used as the subject of a sentence. Examples: I, you, he, she, it, we, they.
* Objective pronouns are used as the object of a verb or preposition. Examples: me, you, him, her, it, us, them.
Example:
* "The dog wagged its tail." (Here, "its" shows that the tail belongs to the dog.)