A hidden object cannot be referenced. It is not addressable. It cannot be found. It cannot be named. Visibility of an object carries with it a name, or handle, for the object so that it can be identified.
Identification is the basis for distinguishing the object from others.
The other part of visibility is addressibility. Addressibility is the property that allows two objects to actually touch each other. The addresses do not have to be explicit, such as a MAC address, but can be implicit such as when two strangers communicate. The addressing, in the second case, can be as simple as eye contact. While visibility is the most obvious property required for availability, another fundamental property is reachability.