Federal Reserve Governor Stephen Miran entered with big ideas about how the central bank should change— radically so, in some cases. As he prepares to step down in the coming days from what will have been the shortest tenure as a governor in 71 years, he appears convinced his ideas are right. But in a CNBC interview, Miran, 42, made clear that the reality of working at the Fed has tempered his views about how fast those changes can be made. Change is slower than he envisioned. The Fed is "