I cannot reveal too much here and now because today's column is not yet up on Barron's Online but the topic was a comparison of the chart of the stock market today a time period in the past - called an analog. These sorts of comparisons often look great on paper when they are made but tracking the market's two time periods does not always give you a good path to follow.
There are so many factors in play that any one of them can rise from being a non-influence to being the major tipping point. For example, ask a trader a few years ago what high frequency trading (HFT) was. You would ave gotten a blank stare.
Ditto zero percent interest rates or even a war on terror with its requisite changes in how business gets down (air travel, new security industries, protection of the power grid, etc...)
Anyway, more on the column after it is up on the site.