Here's why:
* Proper nouns are specific names of people, places, or things (e.g., John, London, Eiffel Tower).
* Common nouns are general names for people, places, or things (e.g., man, city, building).
"Origami" is a Japanese word that refers to the art of paper folding. It's a common noun because it describes a general concept, not a specific person, place, or thing.