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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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his Motley Fool CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy assures you no Wookiees were harmed in the making of this article.