Here's why:
* Abstract nouns refer to concepts, qualities, or ideas that cannot be touched or seen. Examples include love, happiness, justice, freedom.
* Adjectives describe nouns or pronouns. They tell us more about the qualities or characteristics of something.
"Careful" describes how someone is doing something, like "a careful driver" or "a careful reader." It's not a concept in itself, but a quality that can be applied to people or actions.