Here's why:
* Common nouns refer to general, non-specific people, places, or things.
* Proper nouns are specific names of people, places, or things (e.g., John, Paris, Eiffel Tower).
"Trip" is a general term that refers to any journey or excursion. It doesn't specify a particular trip.
For example:
* "I took a trip to the mountains." (general, common noun)
* "The trip to Disneyland was memorable." (general, common noun)
We can use "trip" to refer to many different journeys, making it a common noun.