The Cardinal Rule of Military Strategy, as I see it, is to expect the military forces of a nation to try to do what they have done very well before. In other words, when a nation has won a great military victory, it cannot help but try to repeat that victory in later combat.
Let's look at a few examples.
In 1940, the Nazis made a successful thrust with tanks through the Ardennes Forest in Belgium and Luxembourg. The British and French had presumed that it was not possible to move a large force of tanks through a dense forest.
Four years later, the fortunes of the war had changed but the battle front was at the same place. Once more, the Nazis launched an attack with a large force of tanks through the Ardennes Forest. This time, it was Americans that were taken by surprise and the result was what is commonly known as the Battle of the Bulge.
The failure to anticipate that the enemy might try a move which they had done so successfully a few years previously sheds a light on my Cardinal Rule of Military Strategy. If the Nazis had made such a successful attack using tanks through this forest before, why wouldn't they try it again?
On to another prominent example. The real turning point of the Second World War in Europe was the Battle of Stalingrad. The Soviet forces managed to sorround and trap the German Sixth Army and associated units in the city of Stalingrad. The final result was a great victory.
After the war, the alliance between the Soviets and the western Allies cooled into the Cold War. Stalin decided to cut off access to West Berlin, which was an enclave of West Germany within East German territory. The Communists forbade access by road to West Berlin and harrassed the Allied aircraft which were trying to supply the isolated city. The hope seems to have been that the Allies would just abandon the city to the Communists.
What could this be but an attempt to replicate the victory at Stalingrad a few years earlier, in which the Communists had managed to sorround the enemy?
In 1905, a newly modernized Japan won a great naval victory over Russian forces in the sea adjacent to Korea. What was the Pearl Harbor Attack forty years later but an attempt to repeat this victory?
In World War One, German forces had considerable success in the campaign against Russia, which ultimately underwent the Bolshevik Revolution of 1917. Why didn't Stalin anticipate that they would be sure to attempt a repeat, which came with the invasion of 1941?
The amphibious landing by the Allies at Inchon during the Korean War looks very much like an effort to replicate the series of amphibious landings on the coast of Italy during the Second World War a few years before. Korea consists of a peninsula which resembles that of Italy and the most obvious way to break a combat deadlock is such a landing behind enemy lines.
If the Vietnamese Communists had successfully overcome the French forward base at Dien Bien Phu, then why wouldn't they try a similar assault against the American forward base at Khe Sanh? Which they did during the Tet Offensive of 1968.
Movies can also play a role in the Cardinal Rule of Military Strategy. If a secret operation to rescue a hostage worked so well in the 1969 movie "Where Eagles Dare", why wouldn't a very similar operation work in real life to rescue the American hostages being held in Iran in 1980? Am I the only one to notice the very close parallels between this movie, especially the chase scene at the end of the movie, and "Operation Eagle Claw" to rescue the hostages?
The victory being emulated does not necessarily have to belong to the nation which is seeking to achieve it. A smashing or spectacular victory by one nation is likely to be copied by others in later combat. Let's look at a few examples of this.
The sorrounding of the American Embassy in Saigon, then the capital city of South Vietnam, in 1975 was a real debacle for the U.S. as it tried to evacuate as many people as possible by helicopter to ships off the coast as the world watched the fall of the country on television. Is it only a coincidence that four years later, Iranian mobs seeking to humiliate the United States would launch an attack on it's embassy?
In 1967, Israeli forces were heavily outnumbered as war neared. But an aggressive and well-coordinated blitz turned everything around in what became known as the Six-Day War. Four years later, India decided to intervene in the West Pakistani effort to subdue a rebellion in East Pakistan (now Bangladesh). The Pakistani response was very reminiscent of the sudden Israeli blitz, particularly the thrust which resulted in the Battle of Longewala.
I don't think that suicide terror tactics are originally Islamic at all. They are a copy of the kamikaze and banzai tactics of the Second World War.
Once again, we come to movies. We know that the 9/11 attack of 2001 had been in the planning stages for about five years. Two movies that were very popular in 1996 were "Independence Day" and "Pearl Harbor". Why do I have the feeling that this is no coincidence?
In summary, The Cardinal Rule Of Military Strategy is to anticipate that the enemy will try to repeat what they have done well in previous combat. They may also imitate a smashing victory in recent memory by another nation, or even a plot from a movie. I don't think that there is any rule of combat that can be considered as more important than this.