Deterrence is not a security objective and do not count on it when you build your security doctrine, plan, procedures for effective prevention and/or neutralization tactics for adversary threats.
The wishful thinking prophecy that stems from the creation of a deterrent policy is not based on effective security tactics. Rather, it is based on probability and is dependent on the adversary motivations and capabilities. Therefore a security culture should be based on interfering with the adversary motivations and capabilities. It is the combination of proactive security methodologies, offensive intelligence and a robust security apparatus that may or may not deter an adversary. But this prophecy is unimportant!!! It is unimportant because your security apparatus should produce results regardless of deterrence! Instead it should function as if deterrence does not exist!
This reality is often unappreciated by security professionals because it requires facing the threat at its root and not treating the symptoms. But there are no shortcuts and Europe and the US will eventually reach this intersection. It is not about reaching the intersection but rather crossing it and continuing to drive forward.
The crossing of the intersection requires the building of an offensive security apparatus that is designated at providing early warning, strategic surprise of the enemy and rapid elimination of the threat. The investment in the defensive dimension of security alone will only increase the gap in finding strategic and operational solutions and demoralize the resilience of the security forces and citizens.