Yamamoto's philosophy was defined by a single, terrifying constraint: Time. He was a master of asymmetric warfare before the term existed.
Yamamoto knew Japan could not win a resource war. His only hope was a "Short War"—a blitzkrieg at sea. If he could destroy American naval power in 24 hours, perhaps American political will would collapse before their industrial capacity geared up.
Traditionally, battleships ruled the waves. Yamamoto, an aviator at heart, argued that the battleship was obsolete. "The fiercest serpent may be overcome by a swarm of ants," he said. He built the Kido Butai—the mobile strike force of six fleet carriers—which became the most powerful naval weapon on earth in 1941.
Yamamoto loved poker, shogi, and bridge. He would bet on anything. This "gambler's mindset" bled into his strategy. At Midway, he split his forces into four widely separated groups—a complex, high-risk play that assumed the Americans would react exactly as he predicted.
In gambling, this is called "playing the player, not the cards." Yamamoto thought he was playing against a timid, demoralized American fleet. He was wrong. He was playing against Nimitz, Spruance, and—crucially—Codebreakers who were reading his mail.
Yamamoto is a tragic figure. He was the only man in Tokyo who truly understood the enemy, yet he was the one tasked with starting the war he knew would destroy his country. He died exactly as he predicted: in a ball of fire, before the final defeat, spared the sight of the burning cities he knew were coming.