If there's one lesson entrepreneurs can learn from last week's Wall Street meltdown it's that every business needs a long-term, viable model to remain profitable. As news continues to come in about what went wrong at Lehman and even Bear Sterns, it's increasingly apparent that these huge firms that should have had a rock solid business plan with a strategy for long-term profitability did not. But, why? It appears that while things were going well, no one wanted to touch what they perceived as a good thing—including regulators. In article in last week's New York Times sums it up well:

"Had the S.E.C. gone over the records of Lehman and Bear Stearns with the vigilance it now promises for the shorts, we might not be in this mess. It is a sad commentary that the authorities are most worried about a market that they were unwilling to do anything about when it was growing and growing."

While the Times article is more specifically railing against a lack of regulation on Wall Street, it incidentally pointed to a larger issue. These banks were reckless and in many ways didn't consider the long-term impact of their model because at the time it was making everyone buckets of money.

It's a critical lesson for entrepreneurs as well. During flush times, a bleak and less profitable future can seem impossible to fathom. But it's a reality that most businesses face. The market will always have ups and downs, and if you let things slide while things are good, the down times can be disastrous. What that means is keeping a check on expenditures and cost. Maintaining a strong marketing budget. And above all else, ensuring that even if the market drops and consumer spending declines, that you still have a model for remaining profitable.

Obviously Lehman and Bear's troubles ran far, far deeper than that. But a total lack of long-term planning seems to have played some role. They learned the lesson the hard way.