Here's why:
* Concrete nouns refer to things that can be touched, seen, heard, smelled, or tasted. They are physical and tangible. Examples: book, chair, apple, smell, sound.
* Abstract nouns refer to ideas, concepts, qualities, or feelings. They are intangible. Examples: happiness, love, justice, freedom, literature.
Literature represents a body of written works, which is an idea or concept, not something you can physically touch or experience.