One of the challenges of writing in tight third person is that you can get so swept up in seeing the plot unfold through your protagonist's eyes, you forget what you know that they don't.
This happened to me today. I was cruising along, at 800+ words for the day, feeling a little smug about how smoothly it was going... and then suddenly I thought: Wait a minute. Why would Tom do that? He's too smart to give anyone a reason to suspect he has a hand in what Willa's about to do. So why the hell would he be seen talking to her in front of like a hundred people ten minutes before she does it?
It seemed perfectly logical to Willa when it happened, because Willa doesn't know what Tom knows. She doesn't know how much of a scheming, power-hungry douchebag he is beneath the folksy earnestness. She doesn't know she was part of his plan even before the current situation unfolded. But I know, and I should have seen that Tom is much too savvy to put himself in the position I put him in.
Crap. Now I have to go back and rewrite it. At least it's not the whole scene-- just the last 350 words. I'll still make it to 1,000 tonight.