In her first public speech on monetary policy, Janet Yellen made it clear that the Fed intends to pursue a more rules-based, less discretionary policy. This is good news. The bad news, however, is that Yellen focused only on employment and inflation. In that same speech, not a single word was said about attending to speculative risks or financial instability (which are inherent in Fed-induced, yield-seeking speculation). Without attending to that third leg, the Fed is resting the fate of the U.S. economy on a two-legged stool. The problem is this. In viewing the Fed’s mandate as a tradeoff only between inflation and unemployment, Chair Yellen seems to overlook the feature of economic dynamics that has been most punishing for the U.S. economy over the past decade. That feature is repeated malinvestment, yield-seeking speculation, and ultimately financial instability, largely enabled by the Federal Reserve’s own actions.