We would all like to think that humankind is getting smarter and wiser and that our past blunders won"t be repeated. Bookshelves are filled with such reassuring pronouncements. Encouraging forecasts rest in part on the belief that we can learn the right lessons from the past and cast discredited ideas onto the ash heap of history, where they belong. Those who think that humanity is making steady if fitful progress might point to the gradual spread of more representative forms of government, the largely successful campaign to eradicate slavery, the dramatic improvements in public health over the past two centuries, the broad consensus that market systems outperform centrally planned economies, or the growing recognition that action must be taken to address humanity"s impact on the environment. An optimist might also point to the gradual decline in global violence since the Cold War. In each case, one can plausibly argue that human welfare improved as new knowledge challenged and eventually overthrew popular dogmas, including cherished but wrongheaded ideas, from aristocracy to mercantilism that had been around for centuries. Yet this sadly turns out to be no universal law; There is no inexorable evolutionary march that replaces our bad, old ideas with smart, new ones. If anything, the story of the last few decades of international relations can just as easily be read as the maddening persistence of dubious thinking. Misguided notions are frustratingly resilient, hard to stamp out, no matter how much trouble they have caused in the past and no matter how many scholarly studies have undermined their basic claims. Consider, for example, the infamous " domino theory, " kicking around in one form or another since President Dwight D. Eisenhower"s 1954 "falling dominoes" speech. During the Vietnam War, plenty of serious people argued that a U. S. withdrawal from Vietnam would undermine America"s credibility around the world and trigger a wave of pro-Soviet realignments. No significant dominoes fell after US troops withdrew in 1975, however, and it was the Berlin Wall that eventually toppled instead. Various scholars examined the domino theory in detail and found little historical or contemporary evidence to support it. Although the domino theory seemed to have been dealt a fatal blow in the wake of the Vietnam War, it has re-emerged, phoenix-like, in the current debate over Afghanistan. We are once again being told that if the United States withdraws from Afghanistan before achieving a clear victory, its credibility will be called into question, al Qaeda and Iran will be emboldened, Pakistan could be imperiled, and NATO"s unity and resolve might be fatally compromised. Back in 2008, Secretary of State Condoleezza Rice called Afghanistan an " important test of the credibility of NATO, " and President Barack Obama made the same claim in late 2009 when he announced his decision to send 30, 000 more troops there. Obama also justified his decision by claiming that a Taliban victory in Afghanistan would spread instability to Pakistan. Despite a dearth of evidence to support these alarmist predictions, it"s almost impossible to quash the fear that a single change in their strategy will unleash a cascade of falling dominoes. There are other cases in which the lessons of the past—sadly unlearned—should have been even more obvious because they came in the form of truly devastating catastrophes. Germany"s defeat in World War I, for example, should seemingly have seared into Germans" collective consciousness the lesson that trying to establish hegemony in Europe was almost certain to lead to disaster. Yet a mere 20 years later, Adolf Hitler led Germany into another world war to achieve that goal, only to suffer an even more devastating defeat. Why is it so hard for states to learn from history and, especially, from their own mistakes And when they do learn, why are some of those lessons so easily forgotten Moreover, why do discredited ideas come back into fashion when there is no good reason to resurrect them Clearly, learning the right lessons—and remembering them over time—is a lot harder than it seems. But why The word "discredited" is used twice in the passage. It means______.

A. incorrect
B. shameful
C. reputable
D. rejected