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 coal producer Arch Coal Inc (NYSE:ACI) dropped 10% today after the company reported earnings.

So what: First-quarter revenue fell slightly to $736 million, which was actually well ahead of the $718 million in revenue that analysts expected. But net loss nearly doubled from a year ago to $124.1 million, or $0.59 per share, far greater than the $0.42 loss analysts expected. 

Now what: Coal is facing long-term challenges from oversupply and falling demand, particularly in the thermal market. I don't see these factors changing, and Arch Coal's losses are piling up. Even analysts aren't expecting a profit this year or next and, until we see actual results change, I would stay far away from this stock.

Travis Hoium has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.