Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of regional bank Comerica (NYSE: CMA) took a nosedive after worse-than-expected third-quarter results, shedding more than 10% in intraday trading.

So What: Analysts were expecting Comerica to report earnings of $0.41 per share for the third quarter and the company reported $0.33. Investors tend to be pretty unforgiving when it comes to earnings shortfalls, particularly when they're that sizeable. The market may be reading the soft earnings as a sign that Comerica is having more trouble than expected climbing back out of the recession doldrums.

Now What: I think investors generally tend to pay a bit too much mind to the quarterly pennies per share on either side of analysts' estimates, and I think that's especially true when it comes to the banking industry right now. A quick look at the earnings from Bank of America (NYSE: BAC) and JPMorgan Chase (NYSE: JPM) shows weaker top lines, with bottom lines driven by drastically lower loan-loss provisions -- which are expectations for losses set by management. In other words, a wobbly banking environment combined with significant management discretion on loss provisions makes it extremely difficult to predict banking earnings and renders earnings "beats" and "misses" a bit less meaningful.

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