Because the situations where inflationary pressures are increasing are by their nature usually situations where demand in the economy is running ahead of the economy’s long-term capacity to supply, so that monetary policy aimed at restraining those inflationary pressures inevitably tends to dampen down booms.
And conversely, those situations where demand falls short of the economy’s long-term capacity to supply are usually situations where inflationary pressures are falling towards zero, so that monetary policy aimed at preventing inflation falling below zero (as required by my agreement with the Treasurer) inevitably tends to work to mitigate those downturns.