The art of war teaches us to rely not on the likelihood of the enemy's not coming, but on our own readiness to receive him; not on the chance of his not attacking, but rather on the fact that we have made our position unassailable.
When strong, avoid them.
If of high morale, depress them.
Seem humble to fill them with conceit.
If at ease, exhaust them.
If united, separate them.
Attack their weaknesses.
Emerge to their surprise.