Exceptions represent a breach of an implicit assumption made within code. For example, if your code tries to access a file that is assumed to exist, but the file is missing, an exception would be thrown. However, if your code does not assume that the file exists and checks for its presence first, this scenario would not necessarily generate an exception.
Exceptions are not necessarily errors. Whether or not an exception represents an error is determined by the application in which the exception occurred. An exception that is thrown when a file is not found may be considered an error in one scenario, but may not represent an error.