At the beginning of a campaign it is important to consider whether or not to move forward; but when one has taken the offensive it is necessary to maintain it to the last extremity. However skilfully effected a retreat may be, it always lessens the morale of an army, since in losing the chances of success, they are remitted to the enemy. A retreat, moreover, costs much more in men and materials than the bloodiest engagements, with this difference, also, that in a battle the enemy loses practically as much as you do; while in a retreat you lose and he does not.

Napoleon : In His Own Words (1916)