Interest rates, it has been said, are financial gravity. When rates are high, stock prices should be lower, because they reduce the present value of the future cashflows equity investors lay claims to.
The opposite is also true; when rates are low, stock prices should be higher.
In early November, the market value of the Bloomberg Barclays Global Negative Yielding Debt index rose to a record $17.5trn, eclipsing the previous peak of $17trn in August 2019.
Today, a quarter of the world's investment-grade debt trades with a negative yield.
It is not surprising, then, many investors seeking returns among this harsh environment conclude there is little alternative to equities.
Unlike during the dotcom frenzy or the housing bubble in the run-up to the Global Financial Crisis, the speculative excesses this has spawned are not limited to one industry or sector.
Instead, the mania is more subtle, and reminiscent of the 'Nifty Fifty' era of the 1970s.
The 'Nifty Fifty' was a group of premier blue-chip stocks that became institutional darlings in the 1960s and soared in the early 1970s, before plummeting back to earth in the bear market of 1973-1974.
While there was no definitive list, everyone at the time knew which stocks these were because they tended to share certain common characteristics: a reputation for quality and reliability demonstrated by an ability to operate profitably in good and bad times, with proven growth records and continual dividend increases.
Five decades later, most people are still familiar with household names such as Disney, McDonald's, Procter & Gamble, PepsiCo, Coca-Cola, Pfizer and Johnson and Johnson.
These, and others, were regarded as 'one decision' stocks that could be bought and never sold, because their prospects were so bright and their price-to-earnings (P/E) ratios of 30, 40, or even 70x were more than justified.
In one sense, the buyers were not wrong: a hypothetical equally weighted portfolio would have outperformed over the next 30 years. Eventually, however, the business fundamentals did catch up with valuations.
The difficulty for professional money managers was that over the intervening period they would have endured a savage relative drawdown lasting two decades.