Yi Sun-sin: history’s greatest admiral

When we think of great naval commanders, Nelson immediately comes to mind. He fought 13 battles, winning 8. Admiral Yi Sun-sin fought 23 battles against Japan between 1592 and 1598, and won every one of them without losing a single ship. In 14 of these battles, moreover, not a single Japanese ship survived. How did he accomplish so much, and why was Japan unable to defeat him?