The reason is that when you go from an inflation rate of 2% to 0%, in a context where you have a lot of output gap, firms with excess capacity will try to underprice their competitors, and they can do so by reducing their prices, which means that inflation will fall below zero on aggregate. You go quickly into a deflationary risk scenario.
So very low inflation in the presence of economic slack is a dangerous cocktail. Is it possible that we are there already? What we say is that the risks of de-anchoring have increased, obviously. And that is why we acted forcefully. We have seen in some countries some signs of de-anchoring in wage formation.