Whenever investors are unable to rationalise market trends, they resort to cliché. The latest hoary old chestnut to be trotted out to justify extraordinarily robust equity valuations (until last week, at any rate) is that all bull markets climb “a wall of worry” – a platform of problems that perversely boosts stock prices to fresh highs.

There is doubtless something to the “wall of worry” conceit. There are certain successful investors (one thinks of the likes of George Soros, John Templeton and Marc Faber) who have spun widespread disenchantment about market returns into gold. It is easier said than done, for example, to buy when there is blood on the streets. But heuristics, those rules of thumb that traders use as shorthand to parse the financial runes, can only take us so far. And there are times when widespread conventional fears about the market’s prospects will turn out to be wholly justified. Now feels like one of those times.