Here's why:
* Nouns are words that name people, places, things, or ideas.
* Pronouns are words that stand in for nouns.
Examples:
* Noun as direct object: "The dog chased the ball." (Ball is a noun, the direct object of the verb "chased")
* Pronoun as direct object: "She ate it." (It is a pronoun, the direct object of the verb "ate")
Let me know if you have any other questions!