""appear weak when you are strong" That only seems useful if you want to lure the enemy into an attack in order to ambush him" No, it is also good (necessary)

""appear weak when you are strong" That only seems useful if you want to lure the enemy into an attack in order to ambush him" No, it is also good (necessary) for preparing a good offensive. If the enemy thinks you are weak in some area, he does not expect a push from that direction. Ukraine did just that last fall very succesfull. Show off force and big noisy preparation of a offensive south and starting it loud. And then push hard, fast and unexpected in the north, after the enemy already moved more troops further south. And then confusion and panic among the enemy, so a relativly small force could conquer vast lands.