Here's a rejoinder to the frequent argument, made to tear down an established "great person", by saying, "Well, they weren't all that great; after all, their competition was second rate. They were just lucky":
(NOTE: The source is G. F. Henderson's Stonewall Jackson and the American Civil War, published sometime in the early 20th century; exact date unknown)
"By the ignorant and the envious success in war is easily explained away. The dead military lion, and, for that matter, even the living, is a fair mark for the heels of a baser animal. The greatest captains have not escaped the critics. The genius of Napoleon has been belittled on the ground that each one of his opponents, except Wellington, was only second-rate. French historians have attributed Wellington's victories to the mutual jealousy of the French marshals; and it has been asserted that Moltke triumphed only because his adversaries blundered. Judged by this rule few reputations would survive. In war, however, it is as impossible to avoid error as it is to avoid loss of life; but it is by no means simple either to detect or to take advtange of mistakes. Before both Napoleon and Wellington an unsound manuever was dangerous in the extreme. None were so quick to see the slip, none more prompt to profit by it. Herein, to a great extent, lay the secret of their success, and herein lies the true measure of military genius. A general is not necessarily incapable because he makes a false move; both Napoleon and Wellington, in the long course of their campaigns, gave many openings to a resolute foe, and both missed opportunities. Under ordinary circumstances mistakes may easily escape notice altogether, or at all events pass unpunished, and the reputation of the leader who commits them will remain untarnished. But if he is pitted against a master of war a single false step may lead to irretrievable ruin; and he will be classed as beneath contempt for a fault which his successful antagonist may have committed with impunity a hundred times over."