-1200 · Odysseus, the Greeks, Troy

After ten years of siege, the Greeks left a gigantic wooden horse outside Troy and sailed away. The Trojans, against the warnings of Cassandra and Laocoön, brought the trophy inside their walls and celebrated. At night, the Greeks hidden in its belly opened the gates from within. The defence the Trojans had held for a decade was undone by something they invited in themselves.

The principle: The defence that holds against external attack is often defeated by an invitation. The threat that gets through is the one disguised as an upgrade.

China, Three Kingdoms ~228 CE · Zhuge Liang, Sima Yi

Caught in a city with almost no garrison, Zhuge Liang opened the gates wide, sat on the wall playing his zither, and let Sima Yi's vastly superior army approach. Reading the calm as bait for an ambush, Sima Yi withdrew. The fort was indeed empty — the calm was the entire defence.

The principle: When you can't actually meet the threat, the credibility of your composure can do the work that strength would have done. The opponent reads your apparent confidence as evidence of hidden capability. This works once, against careful opponents — and fails catastrophically against careless ones. Calculate which kind you're facing.

1628 · King Gustavus Adolphus, Master shipwright Henrik Hybertsson

King Gustavus Adolphus wanted Sweden's new flagship Vasa to be longer, taller, more heavily armed with two gun decks instead of one — added during construction. The shipwright knew the proportions were wrong but the king insisted. The Vasa sailed on her maiden voyage in August 1628 and capsized within twenty minutes of leaving Stockholm harbour. She had not yet cleared the city.

The principle: Specifications added after the design is locked accumulate into ships that cannot float. Each request seems individually reasonable to the requester; the catastrophe is in the sum. The role of the engineer is to refuse the sum even when refusing each individual request is impossible.

1972 · Richard Nixon, Mao Zedong, Henry Kissinger

Richard Nixon had built a career on anti-communism. In 1972 he flew to Beijing and shook hands with Mao Zedong, opening US-China relations. A Democratic president would have been destroyed by the right for the same move. Nixon's anti-communist credentials inoculated him against the accusation — only he could go to China.

The principle: Some moves can only be made by the person least expected to make them. Their established position protects them from the attack the move would otherwise draw. The contrarian move is most often available to the most credentialled incumbent of the orthodox position.

2000 · Reed Hastings, John Antioco, Blockbuster

In 2000 Reed Hastings flew to Dallas and offered to sell Netflix to Blockbuster for $50 million. Blockbuster's CEO laughed him out of the room. Why would the dominant video-rental empire pay for an unprofitable mail-order DVD startup? A decade later Blockbuster was bankrupt and Netflix was worth billions.

The principle: When a small threat asks to be bought, it is offering a much better price than it will charge later. Dismissing it from a position of strength is exactly the position from which the dismissal is most dangerous — because you can afford the deal and you assume you don't need it.