We must shape their beliefs to create a mental image we want. Where you focus, you must pretend indifference. When similar to the competition, emphasize differences. When you are different, you must appear similar. Sun Tzu's saw the need for deception as arising from the reality that we live in a competitive world.
Deception is part of a complete system of competition.
We must assume that the competition is going to try to undermine us. He wants us to undermine that strategy from the beginning. Sun Tzu's view assumes that human nature is fickled. If we say anything directly, people are going to challenge our statements. For example, if you want people to think that a product is inexpensive, we can say that it costs too much, or that it is a luxury product.