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 do-it-all renter United Rentals (NYSE: URI) fell 12% today after the company posted disappointing earnings.

So what: Revenue was up 9% to $523 million but still fell below analysts' expectations of $551 million. The net loss of $20 million, or $0.34 per share, is more worrisome because investors were only expecting a $0.12 loss.

Now what: Construction activity isn’t picking up as quickly as analysts had expected and United Rentals paid the price this quarter. Management sounded confident going forward and is still expecting to increase rates 5% this year. If this were a disappointing profit instead of a disappointing loss I might look for a silver lining, but I would like to see United Rentals move into the black before jumping into shares.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.