Here's why:
* Indefinite pronouns refer to nonspecific people or things. They don't refer to a particular person or thing.
* Reflexive pronouns refer back to the subject of the sentence. They end in "-self" or "-selves" (e.g., myself, yourself, himself, herself, itself, ourselves, yourselves, themselves).
Examples:
* Indefinite: "Everybody is welcome." (This doesn't refer to any specific person, just a general group.)
* Reflexive: "He hurt himself." (The pronoun "himself" refers back to the subject "he".)