Of the many accusations and criticisms that have been hurled at Ben Bernanke, one thing you can't say he is guilty of is not having learned from history. A world authority on the Great Depression and its causes and consequences, he vowed upon taking up his job as the US Federal Reserve chairman that he would never allow it to happen again. And this he did, however future historians and economists will have come to judge his tumultuous eight years as the head of the world's most powerful central bank. But while he did not let history repeat itself in the aftermath of the global financial crisis, his unconventional monetary policy is taking us, for better or worse, into uncharted territory. With three rounds of quantitative easing along with Operation Twist, he has shown that, true to his word, monetary policy is not out of ammunition even if interest rates hit zero. The purchasing of bond and mortgage-related securities under QE has helped keep benchmark rates low. There seems to be no question that QE has put a floor under the collapsing US and global economies. On a GDP per capita basis, the US is now outperforming all the other G7 advanced economies, though unemployment is still high and growth has been disappointing. We have the Great Recession instead of Great Depression 2.0; the former is surely the lesser of two evils. But the problem now is how to unwind QE and the massive expansion of the Fed's balance sheet, which has ballooned from less than US$1 trillion at the time of the Lehman Brothers collapse in September 2008 to almost US$4 trillion now. When Bernanke first talked about tapering in May, the world's financial markets took a dive. Having learned another lesson, he chaired his final Fed meeting this month with the announcement that tapering would be gradual, with the bond buying slowing just US$10 billion per month to US$75 billion. Investors liked his message, as the Dow Jones shot up almost 300 points after the announcement. Since the equities and commodities rout in early summer, markets seem to have digested Bernanke's message that tapering is not the same as monetary tightening. A loose monetary policy with ultra-low interest rates will remain in place for a long time yet. The trillion-dollar question is: when QE completely ends, will the US economy be able to stand on its own two feet?