Balancing Ambition with Realism in Historical Strategy

Are there such things as timeless principles of grand strategy? If so, are they always the same across epochs and cultures? What can we learn from reading the classics, such as Thucydides, Sun Tzu, and Clausewitz? "The fox knows many things, but the hedgehog knows one big thing," according to Isaiah Berlin. Which type makes better strategists, or do you need to be a bit of both? John Lewis Gaddis has some wise and thoughtful answers.