If we now take a look at the subjective nature of War, that is to say, at those conditions under which it is carried on, it will appear to us still more like a game. Primarily the element in which the operations of War are carried on is danger; but which of all the moral qualities is the first in danger? Courage. Now certainly courage is quite compatible with prudent calculation, but still they are things of quite a different kind, essentially different qualities of the mind; on the other hand, daring reliance on good fortune, boldness, rashness, are only expressions of courage, and all these propensities of the mind look for the fortuitous (or accidental), because it is their element.
We see, therefore, how, from the commencement, the absolute, the mathematical as it is called, nowhere finds any sure basis in the calculations in the Art of War; and that from the outset there is a play of possibilities, probabilities, good and bad luck, which spreads about with all the coarse and fine threads of its web, and makes War of all branches of human activity the most like a gambling game.
Carl von Clausewitz, On the Nature of War