It's a start. But only a start. Yesterday's 152-point jump in the Dow brought welcome respite from the relentless selling of the past four weeks.

On the hopeful side, the rally had good fundamental underpinnings, driven as it was by a steep drop in oil prices (down $9 a barrel over the past two sessions). In addition, the devastated financials got a lift from Fed chairman Ben Bernanke, who suggested in a speech that the central bank may extend its emergency lending facilities into 2009.

However, the real proof of the pudding will come in the next two or three days. From a technical standpoint, yesterday's rally fell into the "good but not great" category. Advancing stocks outnumbered decliners on the NYSE by a 2:1 margin, well short of the 3:1 (or better) preponderance I would like to see at a major bottom.

What can we learn from the terrible experience of the past 12 months, in which so many once sound financial institutions have imploded? It will take time to sort out all the lessons. But one immediately comes to mind: You can't automatically assume that a company with a great long-term track record will continue to succeed.

If future conditions are going to be radically different from the past, that track record will no longer apply. It's difficult to envision radical change, but as investors we constantly have to try. It's a large part of understanding the risks we face.

Fortunately, some businesses are less exposed than others to the threat of radical, discontinuous change. A food-and-beverage stock, for example, can enjoy the luxury of adapting gradually to change. I'm currently recommending one such well-known stock to my Profitable Investing subscribers and in this turmoil it's allowing them to get a good night's sleep.

P.S. A giant oak has fallen. Mutual fund legend John Templeton passed away yesterday at the age of 95. As a stockpicker, Templeton had few peers in his lifetime. (He almost single-handedly "discovered" Japan in the 1950s, when the nation and its stock market were rising from the ashes of World War II.) He was also a gentleman of the old Southern school, with a deeply religious streak. May he rest in peace.