There may be several years in which demand growth exceeds the normal pace as it eats into the spare capacity. Once the spare capacity has been wound in, however, actual growth in demand and output has to slow, to match the growth rate of potential supply.
First, when inflation expectations are well anchored, a central bank will not have to worry that expansionary policy to counter a negative demand shock will lead to a sharp rise in expected inflation – a so-called inflation scare – that will then push up actual inflation in the future.