// Example:- Only admin is allowed to edit administrators group.
The question is not between admin and a user who is part of administrator group.
To elaborate further, suppose we have a group called group1 which has less permission that administrator group. We then create a user "anil" and assign him to the group "administrator" so now anil enjoys all rights that adminstrator group has. Now we additionally assign anil to the group - "group1". The expectation would be that anil would continue to have same privilage as before but we found the privilege has decreased. To test this further, we again removed anil from "group1" and the permissions available before was restored.
It seems that adding user anil to group - group1 diminished his rights.