Here's why:
* Proper nouns are names of specific people, places, or things (e.g., "John," "New York City," "Amazon").
* Nicknames are informal names used instead of a person's real name (e.g., "Johnny," "Big Apple," "The River").
Examples:
* "John's nickname is 'Johnny.'"
* "New York City is sometimes called 'The Big Apple.'"
* "The Amazon is known as 'The River.'"
Important Note: The use of single or double quotation marks can vary depending on style guides. However, the most common practice is to use single quotation marks for both proper nouns and nicknames.