I was reading up on cyber deterrence today and ran across this little gem in relation to nuclear deterrence:

Because of the value that comes from the ambiguity of what the US may do to an adversary if the acts we seek to deter are carried out, it hurts to portray ourselves as too fully rational and cool-headed. The fact that some elements may appear to be potentially “out of control” can be beneficial to creating and reinforcing fears and doubts within the minds of an adversary’s decision makers. This essential sense of fear is the working force of deterrence. That the US may become irrational and vindictive if its vital interests are attacked should be a part of the national persona we project to all adversaries.

–Essentials of Post Cold War Deterrence (1995)

Source: http://www.nukestrat.com/us/stratcom/SAGessentials.PDF