The third stratagem of the first chapter, 'kill with a borrowed knife', instructs: when you cannot or should not attack directly, use a third party's strength, an enemy's enemy, an ally's grievance, or circumstances themselves. The received text glosses it with the Spring and Autumn precedent of states maneuvering rivals into destroying one another, the pattern the Warring States diplomacy records (Zhan Guo Ce) made a genre.
The pattern is instantly recognizable in modern dress: proxy wars, planted leaks, astroturfed campaigns, and algorithmic pile-ons. Everyone recognizes the borrowed knife in others' hands and almost never in their own.
The stratagem's cold insight is ontological: agency is legible only at the point of contact, never at the point of origin. Whoever designs the collision is absent from the collision, which is why the canon's last defense against deception is simply asking who profits from the angle of the blade.
If every borrowed knife leaves your hands clean, how would you ever know you were the knife?