Computer security—an end state?

Over the years, a number of fixes have been proposed. Early systems introduced the notion of a privileged state. Concepts such as the reference monitor and the trusted path have been codified. In the network sphere, some swear by encryption, while others deploy firewalls. We have even had a variety of government security standards, such as the Orange Book and the Common criteria. But computers are still being hacked. Why have these solutions not worked?