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 Cablevision Systems (NYSE: CVC) fell off the table just after 10 a.m. ET today, falling 10% as the trading day continued.

So what: Fourth-quarter earnings fell to $60.6 million, or $0.22 per share, from $113.9 million a year earlier. At the same time, revenue grew 7.3% to $1.69 billion.

Now what: Pressure on the company's margins is coming from higher content costs, and the pressure doesn't seem to be letting up. Cablevision said it wouldn't increase rates this year to stem the loss of customers, and investors are concerned about the margin pressure. Cablevision is facing a common challenge of losing cable customers, and investors are worrying about falling margins and fewer customers leading to even lower profits in the future.

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