In the last analysis, Napoleon's defeat can be explained in terms of two circumstances. First, a general decline in the quality of his generalship, shown first in the lack of energy which led to poor supervision of subordinates and repeated failure to intervene personally at the decisive point (as had ever been his practice in the years of his prime); this is also reflected in growing indulgence in wishful thinking concerning the military capabilities of his troops (which he persistently overestimated) and the character of the Tsar (which he consistently underestimated). The second circumstance was the sheer size of the enterprise he attempted to undertake; it is doubtful whether any soldier in history would have achieved a larger measure of success, both in preparatory and executive phases under the military conditions of 1812. But in the words of philosopher Montaigne, quoted by the American historian, Dodge: "Great and distant enterprises perish from the very magnitude of the preparations made to ensure their success." The Problems of space, time and distance proved too great for even one of the greatest military minds that has ever existed, but it was the failure of a giant surrounded by pygmies.
~ D. Chandler, The Campaigns of Napoleon, p. 861.