Men are always more inclined to pitch their estimate of the enemy's strength too high than too low, such is human nature.
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 ClausewitzThe 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.
Carl von Clausewitz