Action in war is like movement in a resistant element. Just as the simplest and most natural of movements, walking, cannot easily be performed in water, so in war, it is difficult for normal efforts to achieve even moderate results.
Carl von ClausewitzThe political object is the goal, war is the means of reaching it, and the means can never be considered in isolation form their purposes.
Carl von ClausewitzTo be practical, any plan must take account of the enemy's power to frustrate it.
Carl von ClausewitzThe difficulty of accurate recognition constitutes one of the most serious sources of friction in war, by making things appear entirely different from what one had expected.
Carl von Clausewitz