If the general be skilful, the spirit of his troops is as the impetus of a round stone rolled from the top of a high mountain. VI EMPTINESS AND STRENGTH Sun the Master said:-- To be the first in the field, and there to await the enemy, is to husband strength. To be late, and hurrying to advance to meet the foe, is exhausting. The good fighter contrives to make the enemy approach; he does not allow himself to be beguiled by the enemy. By offering an apparent advantage, he induces the enemy to take up a position that will cause his defeat; he plants obstructions to dissuade him from acting in such a way as to threaten his own dispositions. If the enemy be at rest in comfortable quarters, harass him; if he be living in plenty, cut off his supplies; if sitting composedly awaiting attack, cause him to move. This may be done by appearing where the enemy is not, and assaulting unexpected points. If we go where the enemy is not, we may go a thousand leagues without exhaustion. If we attack those positions which the enemy has not defended, we invariably take them: but on the defence we must be strong, even where we are not likely to be attacked. Against those skilful in attack, the enemy does not know where to defend: against those skilful in defence, the enemy does not know where to attack. Now the secrets of the art of offence are not to be easily apprehended, as a certain shape or noise can be understood, of the senses; but when these secrets are once learnt, the enemy is mastered. We attack, and the enemy cannot resist, because we attack his insufficiency; we retire, and the enemy cannot pursue, because we retire too quickly. Again, when we are anxious to fight, but the enemy is serenely secure behind high walls and deep moats; we attack some such other place that he must certainly come out to relieve. When we do not want to fight, we occupy an unfortified line; and prevent the enemy from attacking by keeping him in suspense. By making feints, and causing the enemy to be uncertain as to our movements, we unite, whilst he must divide. We become one body; the enemy being separated into ten parts. We attack the divided ten with the united one. We are many, the enemy is few, and in superiority of numbers there is economy of strength. The place selected for attack must be kept secret. If the enemy know not where he will be attacked, he must prepare in every quarter, and so be everywhere weak. If the enemy strengthen his front, he must weaken his rear; if he strengthen his right, his left is weakened; and if he strengthen his left, his right is weakened. Everywhere to make preparations, is to be everywhere weak. The enemy is weakened by his extended preparations, and we gain in strength. Having decided on the place and day of attack, though the enemy be a hundred leagues away, we can defeat him.