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's happening: Electric-car maker Tesla Motors (NASDAQ:TSLA) stock fell as much as 7.2% today. After recovering a bit, shares are currently trading at about a 5% loss.

Why it's happening: After guiding for record quarterly deliveries, Tesla delivered a record, but the number wasn't as big as the company said it was going to be. Tesla fell short of its guidance for vehicle deliveries for Q4 by about 1,400 vehicles, delivering 9,834. After meeting or exceeding guidance for seven quarters in a row, the underperformance took the market by surprise.

While Tesla actually built 11,627 vehicles during the quarter, enough to meet its guidance for about 11,180, the company said it ran into troubles getting those built-to-order cars to customers, citing severe weather, customers being on vacation, and shipping problems.

The shortfall in deliveries negatively affected Tesla's revenue and EPS, causing the company to miss analyst estimates for both. Tesla's inability to meet analyst estimates for top and bottom line likely amplified market pessimism toward the stock.

For more on Tesla's fourth-quarter earnings, check out this earnings brief.