The last two chapters were about counting and ratios. Now, in the chapter on dispositions, Sun Tzu changes the viewpoint. He looks not at the moment of fighting but at the state before it.
昔之善戰者,先為不可勝,以待敵之可勝
xi zhi shan zhan zhe, xian wei bu ke sheng, yi dai di zhi ke sheng
The good fighters of old first made themselves impossible to defeat, then waited for an opening in the other side. (The Art of War, Dispositions, translated directly)
Half of Sun Tzu’s strategy sits inside that one sentence.