Whenever the 100-share Footsie is approaching a number ending with a couple of noughts, unfailingly when there are three noughts in the frame, people who should know better describe the index number in question as "psychologically important".
It is nonsense, of course. The index is an artificial construct. You can bet on it, you can speculate on it with derivatives. Tracker funds try to match it by holding the constituent shares in what they hope is the right weighting. But they do not drive the index - it drives them. There is no market in any index because there is nobody out there trading in it to determine its price.
Anyway, the Footsie 100's contents are changed every three months. Shares that do badly eventually drop out because their market value has become too small. They are replaced by others that have become bigger, usually because they have been doing better.
There is no proper sense in which any index number is important, psychologically or otherwise.
Yet look at what has been happening. For more than two weeks now the Footsie 100 has been hovering around the 6,000 mark for all the world as if there really was some barrier. Each time it nudges above the magic number a flurry of profit-taking knocks the index back below it.
Within a day or two buyers appear to push it back up again.
A chartist would say this is classic behaviour and that when the chart breaks out decisively either up or down you can expect a sharp move in that direction.
There is sense in this with a chart tracing the performance of an individual share. It shows what real money is doing regardless of analysts' chit-chat. But nobody stakes real money to buy an index, only on the shares within it.
Be that as it may, plenty of people will find deep significance in yesterday's closing Footsie number of 6044.1, the highest since February, 2001 - just before the wider market followed the overblown tech and telecoms shares off the cliff.
Not everybody who sets store by these patterns will be persuaded. Some worry that it is highly unusual for any bull market to run for more than three years - although it s tarted from a deeply bombed-out base in March, 2003.
Note, too, that oil and mining shares have been setting the pace this market and there is no reason to see the commodity booms that are driving them running out of puff.
That may not be the case with the wall of cheap money that has been fuelling the present takeover mania. Now that official interest rates in America are higher than ours, there is no joy left in borrowing cheaply there and "carry-ing" the proceeds to some-where - like Iceland - where it earns a fat return, or to fund private equity ventures.
You could see the result yesterday. EasyJet's Icelandic stalker gave up and sold out. Jitters spread to Woolworth and French Connection, both companies where the Icelandic Baugur has built up a stake, though French Connection rallied later.
The game may continue for a while. But it is changing. ..SUPL: