Tesla stock opened the new year by falling 6.8%, after a fourth quarter production update that was a little below expectations, according to Sanford C. Bernstein. Production rose 8% in the quarter, Tesla said, noting that for the full year it delivered 245,240 vehicles—almost as many as it delivered in all previous years. Still, the slight underperformance, along with a $2,000 price cut Tesla announced to offset a reduction in federal tax credits for electric vehicles, could undermine investor confidence after the stronger than expected third quarter. The update makes the fourth quarter financial report even more important. The company had a surprisingly strong third quarter: can it maintain that momentum?