Some common nouns name a thing. Common nouns are never capitalized.
Here are some common nouns that name a thing:
box, shoe, house, rain, ball, book, sofa, bicycle, car, pencil, shirt, nose, dog, computer, phone, banana
Any object can be a common noun. Common nouns are not specific, so they are not capitalized.
It’s your turn. Find two common nouns for a thing in this sentence: John rode his scooter to Grandma’s house. Did you find two unspecific things in this sentence? Good for you.