In general, an economy is in a sweet spot when inflation is low and GDP growth is high, especially when growth has recently started to take off—because the absence of inflationary pressures may suggest it is the beginning of a long run. If GDP growth is picking up but inflation is rising with it, the boom can’t last long because at some point—sooner rather than later—the central bank will have to respond by raising interest rates, in order to dampen demand and subdue inflation.
