Here's why:
* Adverbs modify verbs, adjectives, or other adverbs. They tell us *how*, *when*, *where*, or *to what extent* something is done.
* Adjectives describe nouns.
Example:
* Adverb: She acted responsibly during the crisis. (modifies the verb "acted")
* Adjective: She was a responsible employee. (describes the noun "employee")