If you cannot be strong, and yet cannot be weak, this will result in your defeat.
Plan for what is difficult while it is easy, do what is great while it is small. The most difficult things in the world must be done while they are still easy, the greatest things in the world must be done while they are still small. For this reason sages never do what is great, and this is why they can achieve that greatness.
So it is said that if you know others and know yourself, you will not be imperiled in a hundred battles; if you do not know others but know yourself, you will one and lose one; if you do not know others and do not know yourself, you will be imperiled in every single battle.
What everyone knows is what has already happened or become obvious. What the aware individual knows is what has not yet taken shape. what has not yet occurred. Everyone says victory in battle is good, but if you see subtle and notice the hidden so as to seize victory where there is no form, this is really good.
Getting people to fight by letting the force of momentum works like rolling logs and rocks. Logs and rocks are still when in a secure place, but roll on an incline; they remain stationary if square, they roll if round. Therefore, when people are skillfully led into battle, the momentum is like that of round rocs rolling down a high mountain – this is the force.
Armies are expensive. Fighting is expensive. Failure in battle is irrecoverable.
Know your terrain well.
Know types of terrain well.
Outcome of a war is known before it starts.