Rule of War 1

Wars are never "short."

(Someone will eventually bring up wars of conquest, the blitzkrieg, and the Six-Day War.  The Six-Day War, as we know now, was merely a skirmish in the ongoing Arab-Israeli standoff.  The blitzkrieg stalled out in Russia and was followed by resistance, aerial bombing, the Normandy invasion and surrender.  Five or so years, millions of lives.  Wars of conquest are only brief in the histories; they are an eternity to the survivors.)

In fact, a war's length is in inverse proportion to predictions of its brevity.  (If everyone declares that the war will be short, that war will drag on for years.)

This rule has never been learned.