I in fact read the document as very down to earth as well, and I quoted Yang Chengfu’s use of 守 to amplify what I think is the intended meaning in this song. If there is a flavor of mystery in my translation, it is because of what I think is the operative phase in the Xu Shi Jue, that is: 虛虛實實. That is a formula that specifically addresses strategy, rather than tactics, which is what you are addressing. The phrase 虛虛實實is sometimes translated “feints and ambushes,” and has to do with perception—with what is seemingly false and seemingly real (或虛或實，真真假假).
While at the tactical level it’s important to know clearly what pertains to “me” and what pertains to “the other guy,” at the strategic level it may not be so pat. What keyed me to this understanding is the conspicuous occurrence of the 虛虛實實 formula that most likely accounts for its entry into ordinary language as “feints and ambushes.” It comes from a discussion in the Romance of the Three Kingdoms between Zhuge Liang and Guan Yu about the use of disinformation, deception, or dissimulation (man 瞒). Everyone in the account is familiar with the importance of understanding empty and full, and judiciously quote Sunzi about “using the full to attack the empty” and the like. But on the ground one is faced with appearances meant to lure one into a situation that may be different than one’s expectation. In another passage, Cao Cao asks, “Have you not heard it said in the book of war, ‘If it is hollow [xu] regard it as solid [shi]; if solid, then take it as hollow’?” (quoted in Lisa Raphals, Knowing Words: Wisdom and Cunning in the Classical Traditions of China and Greece, p. 143)
Specifically, the generals are talking about the ruse of building fires on a pass or road to make the enemy think there are soldiers camped there, and thereby divert the enemy to a different route, ultimately to be surprised by the soldiers in their real location. But in a crucial instance, Zhuge Liang anticipates that his opponent will read his actions as a bluff, and turns the tables on him. He explains to Guan Yu: “Have you not heard of the method of warfare of ‘[attacking] the empty with the empty and the solid with the solid [xu xu shi xhi]’? Although Cao Cao is capable in using soldiery [yong bing, in both the human and material senses], this time it is possible to surpass him by the use of dissimulation [man]. When he sees the smoke rising, he will take it as an empty bluff of situational advantage [shi 勢], so he will consider that road trustworthy and proceed.” (again, quoted in Raphals, p. 143)
Here’s the passage from the San Guo Yan Yi where the discussion of 虛虛實實 occurs: http://ctext.org/sanguo-yanyi?searchu=% ... E%E5%AE%9E
As Sunzi said, “Thus an army does not have fixed strategic advantages (勢) or an invariable position (形). To be able to take the victory by varying one’s position according to (因) the enemy’s is called being inscrutable (神). (trans. Roger Ames, Sun-Tzu: The Art of Warfare, p. 127) I suppose that sounds mysterious too, but it’s very down to earth.