Everything that we do in museum security works toward controlling these three things. Locks, alarms, guards, barriers, window protection, etc. These all work toward neutralizing one or more of the basic elements.
The mission of the museum security department is to constantly reduce risks and vulnerabilities. Every resource must be dedicated to controlling these three elements.
If you can achieve Access Control, Parcel Control and Internal Security in a museum, you will have achieved perfect security. If not, all of your losses can be attributed to a failure to achieve one or more of these elements.