This is because when a DML exception is thrown, it means that the operation failed due to some error, such as a validation rule, a trigger, or a governor limit. If the exception is not handled, it will cause the entire transaction to roll back and display an unhandled exception message to the user. To handle exceptions gracefully, the developer should use a try/catch block to catch the exception and handle it in a way that does not disrupt the user experience, such as logging the error, displaying a custom message, or retrying the operation. References: The use of try/catch blocks for handling exceptions is covered under Apex basics on Trailhead1. You can also find more information on DML exceptions and how to handle them in the Apex Developer Guide2.