A colleague with a longer recollection of financial crises than mine says that, when he first came into financial journalism, there used to be something known as "the 40-year rule".
This had it that really serious banking crises only happened once every 40 years, because that was roughly the career lifespan of most bankers - in at 20, out at 60.
It therefore required a full 40 years to wipe out all institutional or salutary knowledge of the previous calamity, thereby creating the next one.
When you think about it, in rough terms the rule actually works.
The last big banking crisis was in the early to mid-1970s.
Prior to that, you have to go back to the Great Depression.
Further back in history, there was another really bad one in the late 19th century, and so on.
Certainly the current crisis is outside most people's experience.
Few of those who work in the City and on Wall Street even properly remember the downturn of the early 1990s, let alone the banking crisis of the 1970s.
George Soros, the billionaire speculator and philanthropist, has described it as the worst financial firestorm since the Great Depression, and we've every reason to believe him.
Yet that doesn't mean it is necessarily going to end in an equal economic implosion.
After another shocking day in stock markets yesterday, partially reversed on Wall Street later on as a result of a sudden fall in the oil price, Kevin Gardiner, equity strategist at
HSBC
, observed that there is no point in arguing with the market in this mood.
Despite corporate and economic fundamentals that are actually not that bad, if confidence in the financial system continues to erode at the present stomach-churning rate it will eventually bring the economy with it.
Markets are in danger of creating a self-fulfilling prophecy.
So far, the policy action taken in the US and elsewhere has failed to underpin confidence in our financial institutions in the manner intended.
Rumour, fear and hearsay continue to rule the roost.
For central bankers, it has been like spitting against the wind.
There are two ways it can go.
Either things will settle after a short and relatively mild downturn, and we'll eventually look back at what's occurred as just another of those temporary, and in some respects necessary, workouts that must always follow a period of excess.
Or it will turn into one of the really bad 40-year events with potentially catastrophic economic and political consequences lasting many years.