Here's why:
* Nouns are words that name people, places, things, or ideas. Examples: *cat*, *school*, *love*, *John*.
* Pronouns are words that stand in for nouns to avoid repetition. Examples: *he*, *she*, *it*, *they*, *we*, *you*, *I*, *this*, *that*.
Example:
* Noun: The cat sat on the mat.
* Pronoun: It sat on the mat.
In this example, the pronoun "it" replaces the noun "cat".