Optimism is a vital attribute when it comes to financial markets.

It can fire up booms far beyond expectations and, occasionally, even the realms of reality.

As we plough on through the fourth consecutive year of global stock records and huge annual advances, it’s not surprising that many pundits have begun to question just how much longer this boom can continue.

Wall Street has only managed this feat three or four times in the past century. The first was the wartime boom from 1942. Then there was the tech boom of the 1990s that unravelled in spectacular style in 2000.

And now this. Since 2019, interrupted only by the war in Ukraine, New York’s main stock index, the S&P 500, has almost tripled, driven by a mere handful of technology giants.