“There is no instance of a country having benefited from prolonged warfare.”
War is expensive in time, resources, and attention, and no one emerges richer from dragging it out. Sun Tzu’s warning applies beyond battlefields: a fight, a lawsuit, a losing investment — the longer it runs, the more it costs, even when you eventually "win."
Chapter 2 is the economic heart of The Art of War: sieges drain the exchequer, long campaigns inflate prices at home, and strength spent on the march is strength missing at the decisive point. Where Chapter 1 asked how to plan, Chapter 2 asks what any campaign costs — and this lesson is its thesis. Sun Tzu writes as a quartermaster before he writes as a general: no nation ever profited from a war that dragged on.
A founder spends eleven months grinding down a rival over a segment both entered early. He wins the segment — into a market the twelve months of price war has scorched for both players, with margins flattened and a third competitor arriving fresh into the wreckage. The victory is real, the ledger is worse than a quick settlement would have been in month two. The war paid nobody but the war.
The lesson is not pacifism — Sun Tzu spends the rest of the book teaching how to fight. It is a duration constraint: fight only battles that end quickly, and structure every engagement so it cannot become a war of attrition. If winning requires years of draining the enemy, the arithmetic has already vetoed the win.