New Zealand was the first, around 1990, to set an explicit numerical inflation target; the model then spread around the world. Aiming for zero would be risky: price indices slightly overstate true inflation, and a little inflation leaves room to cut interest rates in a crisis while keeping deflation at bay. The 2% figure itself is partly a convention.
That's the estimate from a WHO-led study published in The Lancet in 2024, covering the half-century since the Expanded Programme on Immunization was launched in 1974. It works out to about six lives saved every minute, mostly infants. The measles vaccine alone accounts for around 60% of those lives.
According to the World Gold Council, about 216,000 tonnes of gold have been mined in all of human history. Because gold is so dense (19.3 tonnes per cubic metre), it would fit in a cube about 22 metres on each side, roughly the height of a seven-storey building. Strikingly, about two-thirds of it has been mined since 1950.