Openly repair the plank roads, but sneak through the passage of Chencang
míng xiū zhàn dào, àn dù chén cāng
Make the false attack seem bigger than it is, meanwhile take clandestine action to achieve your real goal on another front.
Pretend to care about something that you do not care about, causing the enemy to expend energy and attention to it. Then, when it is convenient, ignore it.
Attack the enemy with two convergent forces:
The first is the direct attack, one that is obvious and for which the enemy prepares his defense.
The second is the indirect attack that the enemy does not expect and which causes him to divide his forces at the last minute leading to confusion and defeat.
In preparation for a confrontation with Xiang Lu, Liu Bang sent his men to repair the main gallery roads (which he had destroyed not long before).
Simultaneously, he secretly marched his main contingent through the small town of Chengcang. Xiang Lu, meanwhile, had relaxed as he knew that the gallery roads would take years to repair.
Liu Bang was hence able to take the lightly guarded Guanzhong by surprise.