Self-reinforcing momentum carried US equities for two years. Now, inertia is pulling them in the wrong direction, says Jonathan Levin for Bloomberg Opinion. MIAMI, Florida: A self-reinforcing momentum has carried the US stock market higher for more than two years. Since the bear-market low in October 2022, the S&P 500 Index has returned an extraordinary 67 per cent. The more stocks went up, the more investors around the world believed that they would continue to go up. Unfortunately, that self-