From Sun Tzu – The art of War
The commander is the country’s bulwark. His proficiency in war can make the country strong, his deficiency makes it weak. There are three ways by which a commander can bring disaster to his army.
One, he arbitrarily orders his army to advance or retreat when in fact it should not, thus hampering the initiative of the army.
Two, he interferes with the administration of the army when he is ignorant of its internal affairs, thus causing confusion among the officers and men.
Three, he interferes with the officers’ command; unaware of the principle that an army should adopt different tactics according to different circumstances. This will create misgivings in the minds of the officers and men.
When an army is confused and fraught with misgivings, neighboring states will take advantage of the situation and attack. This will help disrupt the army and help the enemy to win.

--- Sun Tzu’s ART OF WAR, Making assessments.

The strength of an army does not lie in mere numbers. So long as long as you concentrate your own sources, have a clear picture of the enemy’s situation and secure the full support of your men that is sufficient. You must win them over by them humanly and keep them in line with strict military discipline. This will ensure their allegiance.

--- Sun Tzu’s ART OF WAR, Deploying the troops.

The guiding principle in military tactics may be linked to water. Just as flowing water avoids the heights and hastens to the low land, and army should avoid strengths and strike weaknesses. Just as water shapes itself according to the ground, and army should manage its victory in accordance with the situations of the enemy. Just as water has no constant shape, so in warfare there are no fixed rules and regulations.

--- Sun Tzu’s ART OF WAR, Xu Shi.