Scratch the surface

Scratch the surface is an idiom that is been in use for over a hundred years. An idiom is a commonly used word, group of words, or phrase that has a figurative meaning that is not easily deduced from its literal definition. Often using descriptive imagery or metaphors, common idioms are words and phrases used […]
from Grammarist
https://grammarist.com/idiom/scratch-the-surface/