Everything is very simple in war, but the simplest thing is difficult. These difficulties accumulate and produce friction. The friction arises because every action in a war depends on each individual involved. This theory of friction was created by Carl von Clausewitz.
He argued that in a war, decisions are made with three-fourths of the needed information hidden in a fog of uncertainty. As a result, the best plan of action may fail due a mental lapse, a mistake, or a misunderstanding of a single individual.