Unix files belong to a user and a group. This creates three levels of authorization hierarchy:

• Owner: The UID associated with the file
• Group: UIDS that belong to the GID associated with the file
• Others: Everyone else

Different permissions can be specified for each of these groups, and these permissions are usually decreasing from owner to others. It does not make sense that the owner of a file has less permission on it than its own group or the users outside that group.