Without predators, the species that is the best competitor for food, shelter, nesting sites, and other environmental resources tends to dominate and exclude the species with which it competes.
If access is denied to a Web service, for instance, the Web service is not executed by the Web server, and therefore the request is never even seen by the Web service.
If there is a deny or specify rule in place for a user that denies access, even if the base permission gives access by user or group, the user is denied.
It has always bothered me when I or a fellow workmate requested a transfer only to have the request ignored or denied, seemingly without any thoughtful consideration.