The author says “The basic idea of a Defensible Security Posture is that you aren’t striving for an absolute, but rather for a position (or posture) that is able to be defended even when it’s infiltrated.” This makes a great deal of sense in the face of increasingly sophisticated attackers who benefit from a playing field where the attack surface keeps growing as more of our precious digital assets go online.
Read this multi-part article, starting with Part 1 here:
http://nigesecurityguy.wordpress.com/2013/06/04/defensible-security-posture/