It is well to know a fact in general terms, even if we do not know it in precise terms: it is well to know in general terms that we must not take prussic acid, even if we do not know exactly how much is needed to kill.
So the studies and problems instituted by Von Moltke, and copied in all the armies and navies of the world, have brought about a science of strategy which is real, even though not exact, and which dwells in the mind of each trained strategist, as the high tribunal to which all his questions are referred and by whose decisions he is guided; just as the principles of medicine are the guide alike of the humblest and the most illustrious practitioner, wherever the beneficent art of medicine is practised.
It is clear that, in order to be skilful in strategy (in fact, in any intellectual art), not only must a man have its scientific principles firmly imprinted on his mind, but he must make its practice so thoroughly familiar to his mental muscles that he can use strategy as a _trained_ soldier uses his musket--automatically.

Inasmuch as any man requires years of study and practice--say, of chess--in order to play chess well enough to compete successfully with professional chess-players, it seems to follow that any man must require years of study and practice of the more complicated game of strategy, in order to play strategy well enough to compete successfully with professional strategists.

The game of chess looks easy to a beginner; in fact, the kind of game that he thinks chess to be is easy.

But after he has learned the moves, he finds the intricacies of the game developing more rapidly than he can master them, and discovers that chess is a game which some men spend their lifetime studying.

The full realization of this fact, however, does not come to him until after defeats by better players have forced into his consciousness the almost infinite number of combinations possible, the difficulty of deciding on the correct move at any juncture, and the consequences that follow after wrong moves.
So with strategy.