The core premise is that war is the way of deception. You win by creating illusions. Appear weak when strong. Appear strong when weak. Appear far when near. Appear near when far. The enemy moves to shadows. You hit where he is not.
The problem is cost. War drains the state. Prolonged war ruins armies. It angers people. It empties treasuries. A wise general avoids long war. He wins fast. He wins cheap. He wins without fighting if possible.
The book offers a reframe. Do not seek battle. Seek advantage. Shape the enemy. Do not be shaped. Force the enemy to react to you. Do not react to him. The goal is not glory. The goal is survival of the state.