窮寇勿追 Never Chase A Cornered Foe
他們在豹頭山戰鬥多時，那妖精抵敵不住，向沙僧前喊一聲：「看鏟。」沙僧讓個身法躲過。妖精得空而走，向東南巽宮上，乘風飛去。八戒拽步要趕，行者道：「且讓他去。自古道：『窮寇勿追。』且只來斷他歸路。」八戒依言。他们在豹头山战斗多时，那妖精抵敌不住，向沙僧前喊一声：「看铲。」沙僧让个身法躲过。妖精得空而走，向东南巽宫上，乘风飞去。八戒拽步要赶，行者道：「且让他去。自古道：『穷寇勿追。』且只来断他归路。」八戒依言。
逐句解 Line by line
They had fought a long while on Leopard-Head Mountain when the fiend, unable to hold out, shouted in front of Sha Monk, "Look at my spade!"
The shout is a feint, and an old one — call attention to the weapon so the other man watches it. Sha Monk is the one he picks, which suggests he has worked out which of the three is the least dangerous.
Sha Monk gave way with a turn of his body and dodged it.
Eight graphs, and the trick fails. 讓 here is to yield ground rather than to permit — he steps aside instead of blocking.
Getting his opening, the fiend made off, and rose on the wind toward the south-east, in the quarter of the Xùn trigram.
The compass bearing here comes as a trigram, the same system that named the market where the two wolves stopped for a drink — that one stood in the north-west quarter, this flight goes to the south-east. The novel likes to place its geography on that eight-point wheel, and the direction is not idle: Bamboo-Node Mountain lies that way.
Eight Rules stretched out his stride to give chase, but Pilgrim said, "Let him go.
拽 is yè here — the reading recorded for this phrase, and the sense is to draw the stride open, to lengthen it, rather than to drag anything. The rime books give the graph no reading at all that would match the everyday modern word for tugging, and the dictionary's own example of the sense is a body pulling itself back.
"There is an old saying: do not press a cornered enemy.
This is a real maxim from the military classics, and it is still in daily use — the counsel is that an enemy with nothing left to lose fights harder than one with a way out. Pilgrim is quoting the strategists at his brother, which is a slightly grand thing to do about a lion running away.
"Let us just cut off his road home instead."
And here is why he really let the monster go. He is not being cautious; he is choosing to destroy the cave rather than catch its owner. Whether that counts as strategy or as something harder is a question the chapter leaves open.
Eight Rules did as he was told.
Four graphs. For once he does not argue, and the chapter moves straight to the burning.
Pilgrim quotes a maxim about not pressing a cornered enemy, and then does something a good deal less merciful than chasing him. The saying is genuine and old, and it is used here as cover for a decision that has nothing to do with caution.
Cutting off the road home means the cave, and the cave means everything in it. The next passage is short, brisk and total: the small fiends, the goods, the buildings. Pilgrim decides all of it in a single line of quoted wisdom, and his brothers do not question it.
The trigram bearing is the detail to hold on to. Twice now the novel has fixed a location by the eight-point wheel — a market in the north-west quarter where two wolves stopped for a drink, and now a flight to the south-east. The second is where the grandfather lives, and where the next chapter comes from.