The cult of the offensive.

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Israel suffers from the cult of the offensive, which also afflicts the U.S. military. Believing that grabbing the initiative and taking the fight to the enemy wins wars, both of these militaries have stumbled into the tar pit of fighting wars that only guerrillas could love. Both Israel and the U.S. militaries should have known the potency of defensive guerrilla warfare tactics from their prior experiences in Lebanon and Vietnam. But both were arrogant in thinking that their forces should not "slum" by training to fight against such rag tag enemies—even though it was fairly clear that politicians with no military training would be oblivious to the internal contradictions of counterinsurgency warfare and would once again order them to undertake it.

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'Superpowers' have learned this hard fact over and over again since Roman times. Insurgents, freedom fighters, Mujaheddin, call them what you will, learn to wage war on the cheap. Eventually it's costs the superpower, be it monetarily, in lives, or political influence, more than they are willing to spend to keep the occupation going. A great article on how unprepared we are to fight the wars we start.

Tip o' the Brain to Dave Johnson.