Definition
Weak vs strong points is the central operational principle of Topic 6 of The Art of War. In Sun Tzu's framing, strength is not absolute but relational: it is whatever the enemy must defend against; weakness is whatever the enemy forces you to defend. The strategist's job is to avoid the enemy's strong points and strike where he is weak.
The most famous formulation: "the formation of the troops is like water. Just as water's flow avoids the high ground and rushes to the low, so too the victor avoids the enemy's strong points and strikes where he is weak."
The corollary is arithmetic: "If our army is united and the enemy's divided, that is using a force of ten to attack one." A smaller total force, concentrated against a dispersed larger one, becomes locally larger. The trick is causing the dispersion — and Sun Tzu's mechanism is to make the enemy prepare against threats in many directions at once: "to be prepared everywhere is to be strong nowhere."
Why it matters
How it works
The principle operates by information asymmetry. If you know where the enemy is strong and weak, and they do not know where you will strike, you can concentrate your force at their weakest point. The asymmetry is engineered through concealment of your own intent and revelation of theirs. Sun Tzu spends much of Topic 6 on the mechanics — provoking the enemy to reveal his form while keeping yours hidden, making him prepare against threats everywhere so that each individual point is thinly defended.
The most important corollary is the discipline of deliberate weakness. An organisation that tries to be strong everywhere is strong nowhere — its total resources are spread too thin. The strategist deliberately concedes ground in places that do not matter, so that the places that do matter can be overwhelmingly strong. This is the hardest part of the principle to internalise: it requires admitting that some battles will be lost on purpose.
The water metaphor at the topic's close adds the dynamic dimension: the army with the right form for each contest takes no constant shape; it adapts to the configuration of the enemy. Yesterday's winning formula will be answered by an opponent prepared against it. Each contest demands its own response.