Interest rates had never gone below zero in a major economy, and we did not know how purchasing government bonds would play out in our bank-based economy. These measures represented uncharted waters in which, by definition, the effects of our actions could not be known with certainty.
Nevertheless, these decisions were guided by the evidence available to us, and by an assessment of the overall balance of risks and the options available to respond to them. The evidence at that time pointed in one direction: without new unconventional measures, the ECB would not be able to fulfil its price stability mandate.