Thus, then, in strategy everything is very simple, but not on that account very easy. Everything is very simple in war, but the simplest thing is difficult. These difficulties accumulate and produce a friction, which no man can imagine exactly who has not seen war.

As an instance of [friction], take the weather. Here, the fog prevents the enemy from being discovered in time, a battery from firing at the right moment, a report from reaching the general; there, the rain prevents a battalion from arriving, another from reaching in right time, because, instead of three, it had to march perhaps eight hours; the cavalry from charging effectively because it is stuck fast in heavy ground.