It's things like these ...

• Midway through the second quarter, after the Cowboys backed the Steelers up to their 6 and forced them to punt from the 5, Tra Battle found a way to run right into a short kick from Pittsburgh's Mitch Berger, making the ball live and allowing Lawrence Timmons to recover it at the Steelers' 41. Dallas did force the Steelers to punt, but the miscue wound up magnifying the effect of a Tony Romo interception on the next series. Just three plays after the interception, a third-down stop by the defense was negated by a penalty (12 men on the field), which was followed by a neutral-zone infraction by Tank Johnson. All of that only cost the Cowboys three points.
• Later, in the fourth quarter, veteran Greg Ellis lined up in the neutral zone, turning a tough third-and-6 into a quite manageable third-and-1 for Pittsburgh. A big goal-line stand followed, so maybe Dallas didn't really pay for that one, either.

But to file these things away as irrelevant would be to miss the mark -- by a mile.

In December, the margin for error shrinks. The game is tighter, the stakes higher, each play more important.

There are only so many mistakes you can make. The Steelers' defense was going to make plays. Everybody knew that.

The Cowboys also had to know that helping Pittsburgh -- in the form of mental mistakes and unforced penalties -- would bury them. And it did, just like it has in the past.

And so a strong effort against a strong team circled the drain.

"We had a lot of respect for them, but we felt like we could come up here and win," said tight end Jason Witten, who took the blame for Tony Romo's backbreaking interception in the fourth quarter, which Pittsburgh's Deshea Townsend returned for the game-winning touchdown. "I thought overall, we hung in there. We fought through it."

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In the big picture, sometimes you can't prevent a defense like Pittsburgh's from making a play. Townsend, who said he'd seen the option route from Witten several times earlier in the game -- something that might fall at the feet of offensive coordinator Jason Garrett, not Romo or Witten -- read it perfectly and, had the offensive execution been there, claims he would've broken on it harder.

So go ahead and credit the Steelers for that.

But know this, too: If the Cowboys had taken care of the details earlier on, their margin of error might have been greater. Maybe they could've survived such a blow.

You know, the kind of shot the Cowboys always seem to take on the chin this time of year.

Also on NBCSports.com Rosenthal: Steelers’ struggles could sink their playoff hopes Circling the Bases: Halladay to Cubs? That’s unlikely College Football Talk: Weis to resign? That’s ‘not happening’ Opinion: So far, Nowitzki is NBA’s MVP  |  Fan Ranker Twitter: Follow us @nbc_sports

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