The Art of War has to deal with living and with moral forces, the consequence of which is that it can never attain the absolute and positive.

There is therefore everywhere a margin for the accidental, and just as much in the greatest things as in the smallest.

As there is room for this accidental on the one hand, so on the other there must be courage and self-reliance in proportion to the room available.

If these qualities are forthcoming in a high degree, the margin left may likewise be great.

Courage and self-reliance are, therefore, principles quite essential to War; consequently, theory must only set up such rules as allow ample scope for all degrees and varieties of these necessary and noblest of military virtues.