Final answer:
When trying to add someone to Salesforce who is already there, you will receive a notification or duplicate warning due to Salesforce's duplicate management system, which maintains data integrity by preventing the creation of duplicate records.
Step-by-step explanation:
If you accidentally try to add someone in Salesforce and they are already there, you will get a notification indicating that the record already exists or a duplicate warning. Salesforce has a built-in duplicate management system that prevents users from creating duplicate records to maintain data integrity. When you attempt to add a record that matches the criteria for an existing record in the system, Salesforce's duplicate rules will alert you that a similar record exists. This is helpful because it allows organizations to maintain clean data and avoid confusion caused by multiple entries for the same individual or company.