Regime changes are hard to spot — they only occur every 20 years or so and often slowly, rather than in a single moment. However, financial historians may look back to January 19, 2021 as a key date.

This was when Janet Yellen announced at her nomination hearing to be US Treasury secretary that it was time to “act big” on fiscal easing against a background of near zero interest rates.

Those two words, act big, may come to define the “Yellen moment”, when the economic policy and investment regimes of the past 20 years ended and a new one began — much as Paul Volcker’s 1979 declaration of his fight against inflation as US Federal Reserve chair defined the next two decades. A similar effect on markets was seen when European Central Bank president Mario Draghi declared in 2012 he would “whatever it takes” to save the euro.