Friction is the only concept that more or less corresponds to the factors that distinguish real war from war on paper.

Desperate affairs require desperate remedies.

Our knowledge of circumstances has increased, but our uncertainty, instead of having diminished, has only increased. The reason of this is, that we do not gain all our experience at once, but by degrees; so our determinations continue to be assailed incessantly by fresh experience; and the mind, if we may use the expression, must always be under arms.

[The cause of inaction in war] ... is the imperfection of human perception and judgment which is more pronounced in war than anywhere else. We hardly know accurately our own situation at any particular moment while the enemy's, which is concealed from us, must be deduced from very little evidence.

Knowledge must become capability.

The more physical the activity, the less the difficulties will be. The more the activity becomes intellectual and turns into motives which exercise a determining influence on the commander's will, the more the difficulties will increase.

War is a conflict of great interests which is settled by bloodshed, and only in that is it different from others.