Lucky
and brilliant. Fighting a war utterly outnumbered without much technical or tactical superiority of his troops for years and not losing is an achievement.
By 1756 the Prussian field army consisted of 123.000 men, with 8.000 in reserve and 30500 in garrisons. That high number was never reached again in the Seven Years War. It is, btw, the official number given by the History Department of the Prussian Generals’ Staff (1) Other give
lower numbers, ranging around 145000 men e.g. (2)
Frederick took 62.000 for his invasion of Saxony (3), while the rest were deployed to defend against the threads of Sweden in North, which later indeed landed near Stettin, France and German allied in the west, and Russia in the east, which also came.
The Austrians had 177.444 men, of which 15.700 were border protection (Grenztruppen) (4), others give higher number of 201.000 (5). Initiated by Maria Theresia, who hated Frederick, Leopold von Daun had reformed the Austrian army, so that the quality gap between the infantry of Prussia and Austria had been reduced, if not eliminated. In turn, Frederick’s actions to reform his cavalry were equally successful, so that the Austrians enjoyed only a small, if any, advantage. Quality-wise both armies were close to each other.
The French army (not including the navy) numbered between 200.000 and 213.000 in 1756, depending on the source (6), and around 290.000 by war’s end, of which 140.000 were operating on German grounds, with tens of thousands remaining in France still (7). That is not surprising since the Second Treaty of Versailles obligated France to provide 105.000 troops for an offensive and subside further German allies (8). So anyone saying the French were not fully committed to the war is off the mark. That they made such a poor performance in spite their numbers is hardly the fault of Frederick, but rather a result of his strategy and the great defensive operations of his minor allies.
Russia was less committed that is true, however. Of it’s 172.240 field troops, only 60.000 up to 130.000, depending on the campaign, actually went on the offensive (9). Considering Frederick situation this was more than enough anyway. The first battle was given by some 25.000 Prussians against 55.000 Russians, in August 30 1757 (10).
Of course again, one can argue about the exact numbers that were involved in battle, and Kunersdorf is an excellent example. The Prussian army numbers are quite clear, around 48.000-50.000, including the 7.000 troops guarding Frankfurt a.O. The numbers of the Austro-Russian army vary in the sources, ranging from 79.000 to 60.000. In the best case, Frederick had 10.000 men less than his enemy, in the worst case, he had 31.000 men less. That is quite outnumbered in my book, not "equal odds"!
As for the German minors, the numerical superiority again was against Frederick. Furthermore, one needs to add the 14.000 Swedes who occupied an area near Stettin, right in the back of Frederick.

From: P.H. Wilson: German Armies. War and German Politics, pp.267-286.
It is more than obvious that Frederick was in a situation of sever numerical inferiority throughout the war, with the exception of Saxony’s invasion. The fact that he did survive this situation must be attributed to his strategy. The Russians, French, Austrians did not stop their advances after Kunersdorf – and after years in which whole armies of them were annihilated – because they just did not feel like it, or because they were not so committed… It was Frederick, who still had an operational fighting force, and violently interrupted enemy plans.
One can try to belittle that achievement all day long, but as a matter of fact: in the end he never lost a war.
Btw, Napoleon was one of those envious begrudging men... When he wrote about Frederick, Napoleon always picked the highest number for the Prussians, the lowest for the enemy etc.
To me it is poetic justice that he died as prisoner in middle of nowhere, while Frederick died as the first King
of Prussia, having made his little country a Great Power of his time.
(1) S. Fiedler: Taktik und Strategie der Kabinettskriege, p.141
(2) D. Marston: The Seven Years War, p.20; J. Mollo: Uniforms of the Seven Years War, p.9
(3) S. Millar: Kolin 1757, p.11
(4) Fiedler: op.cit., p.85
(5) Marston: op.cit., p.23
(6) Ibid., p.24; Mollo: op.cit., p.34
(7) H. Delbrück: Geschichte der Kriegskunst, vol.4, bk.3, ch.5
(8) Marston: op.cit., p.35
(9) Ibid., p.22; Mollo: op.cit., p.49
(10) A. Konstam: Russian Army of the Seven Years War, p.4