the short of it:
To be victorious, remember what it’s like to lose.
69. The Practice of Sublime Virtue.
A certain person of military experience has said, “I dare not be the host (to lead on the fight); I would rather be the guest. I dare not advance an inch (to make the first attack); I would rather retire a foot.” Now this (principle if carried out) would, I say, result in there being no following of ranks, no baring of the arm, no charging of the enemy, no grasping of weapons.
There is no calamity greater than making light of the enemy. By making light of the enemy, we are almost sure to lose our treasure. Therefore, when opposing warriors join in battle, the pitiful is always the conqueror.
69.’The Use of the Mysterious (Tao).’
69.1 A master of the art of war has said, “I do not dare to be the host (to commence the war); I prefer to be the guest (to act on the defensive). I do not dare to advance an inch; I prefer to retire a foot.’ This is called marshalling the ranks where there are no ranks; baring the arms (to fight) where there are no arms to bare; grasping the weapon where there is no weapon to grasp; advancing against the enemy where there is no enemy.
69.2 There is no calamity greater than lightly engaging in war. To do that is near losing (the gentleness) which is so precious. Thus it is that when opposing weapons are (actually) crossed, [those] who [deplore] (the situation) [conquer].
69. The Function of the Mysterious.
69.1 A military expert used to say: “I dare not act as host (who takes the initiative) but act as guest (with reserve). I dare not advance an inch, but I withdraw a foot.”
69.2 This is called marching without marching, threatening without arms, charging without hostility, seizing without weapons.
69.3 No greater misfortune than making light of the enemy! When we make light of the enemy, it is almost as though we had lost our treasure (compassion).
69.4 Thus, if matched armies encounter one another, the one who does so in sorrow is sure to conquer.
See Chapter 66 for applicable commentary.