A single exclamation mark is sufficient to indicate strong emotion or emphasis.
Example:
* Wow! That's amazing!
Here's why two exclamation marks are incorrect:
* Redundant: A single exclamation mark already conveys the necessary emphasis.
* Informal: Using double exclamation marks can come across as overly enthusiastic or even childish in formal writing.
However, there are a few exceptions:
* Emphasis in informal writing: In very informal writing (like online chat or social media), you might see double exclamation marks used for extra emphasis, but this is not standard practice.
* Specific situations: There may be specific creative writing situations where using double exclamation marks serves a stylistic purpose, but these are rare.
In most cases, stick to one exclamation mark after an interjection. It's the standard and most effective way to convey strong emotion.