What is the origin of the idiom "diamond in the rough" and when to use it?

The origin of the phrase "diamond in the rough" is uncertain, but it has been used since the 17th century to describe someone who appears ordinary or rough at first, but possesses hidden exceptional qualities or potential. This idiom can be used to describe someone who surprises others with their hidden talents, kindness, or friendly nature. This idiom is often employed in situations where one wants to convey that initial appearances can be deceiving and that there is more to someone than meets the eye.