Among the main reason for the decline of states, history has shown, is overweening self-confidence and arrogance. This was the conclusion reached by Thucydides in his account of the Peloponnesian Wars - considered the first political-military history ever written.

His central thesis, largely accepted by contemporary scholars of ancient history, is that by the 5th century B.C.E. Athens had become Greece's superpower. It practiced democracy (according to the lights of that period), and it enjoyed economic and cultural prosperity, with flourishing literary and art scenes.

But with its success Athens' appetite grew, accompanied by a gravely distorted interpretation of reality. It launched a series of imperialistic wars, including an invasion of Sicily, and ended up surrendering totally to Sparta and its allies, thus setting off political and military decline.

The main reason for this debacle was hubris - a grave sin in ancient Greece - that excessive arrogance that is born of success and that leads those afflicted with it into behaviors that lead them to a bad, bitter end.

The idea is expressed remarkably well by the Biblical phrase "And Jeshurun waxed fat, and kicked" (Deut. 32:15), interpreted as meaning that an excess of good things leads to evil.

An example from personal experience illustrates the phenomenon. In the years preceding the Six-Day War, I was involved in a number of initiatives aimed at improving the decision making process in the government. These included the establishment of the National Defense College; the training of professionals in policy and budgetary planning in the Finance Ministry's school; Levi Eshkol's initiative to set up an Israeli institute for policy studies, and the formulation of a doctrine for managing government ministries.

After the war, all of these activities were suspended. When I asked senior government figures for the reason, I received a simple, clear-cut response: "Look how successful we are, so stop nagging us about flaws in governmental thinking."

Then came the Yom Kippur War. After it, a number of improvements were gradually introduced, such as the establishment of the Planning Division of the Israel Defense Forces, and of a national security team in the Prime Minister's Office (which became the National Security Council), and the reopening of the National Defense College and more.

But the shock of the Yom Kippur War was not enough to remove the fat that was hardening the brain, in the form of illusions about Israel's power. This is because those illusions have profound roots in the heroic success of Zionism and the establishment of the State of Israel, which have almost no historical parallels.

The combination of the miracle of the founding of the state (against the backdrop of the Holocaust, no less), the "miracle" of the Six-Day War and the quasi-messianic meanings both of these events have among the religious and the secular populations is what is responsible for the creation of the illusion that we have developed about our strength.

The gravest results of this dangerous fallacy have been the absence of a worthy effort to exploit the victory in the 1967 war to advance peace; uncontrolled settlement in Judea and Samaria; and the most extreme of all the illusions: the concept of a "Greater Land of Israel."

On top of these illusions there is an seemingly contradictory factor - existential fear, springing from the Jewish people's past and from the confrontation with today's enemies, the Arab states. Paradoxically, this fear combines with the successes to increase the perceptual dizziness about everything having to do with Israel's potential power and its limits, so that delusions of both grandeur and inferiority have evolved.

The practical and paralyzing expression of these two aspects is the hopeless adherence to the idea of the "Greater Land of Israel" among part of the population and support for excessive Israeli surrender of moral and security assets, without appropriate compensation, among another part.

This is the deep reason behind the foot-dragging by the government over peace negotiations, the confusion among the elites, the lack of any authentic spiritual or values-oriented leadership, and the hostility fraught with disaster between the various groups in the population.

This is why Israel cannot take advantage of its strengths in order to secure durable diplomatic-security achievements at the price of giving up on fantasies. Instead, it has placed itself on a slippery slope, at the end of which we will have to make concessions without getting anything in return. We need to sober ourselves up and begin behaving according to the idea that if Jeshurun lost some weight instead of waxing fat, he'd be a lot wiser and kick less.