But she didn't fall on her face. Why did she lose?

Wieber came in third on the U.S. team not because of one big thing, but because of a bunch of little things. Let's go event-by-event.

Vault

On vault, Wieber performs the difficult Amanar vault — that's one-and-a-half flips plus two-and-a-half twists. A couple years ago, hardly any women attempted it in competition, because it's so dangerous. If you don't get your twists around fast enough, you're still twisting as you hit the mat — risking a torn ACL. At the 2011 world championships, Wieber's only Amanar-armed foe in the all-around was her own teammate, Aly Raisman. But since then, everyone else has only gotten better. Everyone on the American team can do an Amanar now. So can a couple Russians. So Wieber lost her advantage there. She scored a 15.833, Douglas scored a 15.9, and Raisman scored a 15.8, shown at left.

Bars

I first started wondering about her chances right after trials, when I was making a GIF guide to the American team. While it was easy to pick the stand-out events for each of her four teammates, it was harder for Wieber. Gabby Douglas runs up her score against Wieber on bars, and Wieber needed to minimize the damage there Sunday. She did not. She made several errors, and scored a 14.833. Douglas scored a 15.333.

Wieber lacks Douglas's natural swinging ability, so she has to do stuff that plays to her advantages -- her massive upper body strength. At left, she's doing two Weiler kips in a row. These take a ton of strength because the centrifugal forces are pulling her body away from the bar. It's a cool trick, but unlike bar elements requiring less strength and better timing and rhythm, which put your body is in the air -- like Douglas's Tkachev to Pak salto combination from Sunday night...

…Wieber's tricks use a lot more energy. She gets tired late in her routine, and makes mistakes, as she did last night. Here, watch how in Sunday night's competition she almost falls off the high bar after her pirouette:

Bars is Raisman's weakest event too. Gymnastics bloggers used to bemoan the death of the sport based on Raisman's bar routine. But in the last year, she's gotten much better. She pointed her toes this time, her legs were straight, she had a good landing on her dismount. Raisman got a 14.1, which isn't good, but it's much better than the horrible 12.9 she got at last year's world's.

(Photo via Reuters.)

Beam

This is one of Wieber's better events -- she got a bronze medal on it at world championships. She's usually very steady. But her routine is constructed in a way that she loses a lot of points if she doesn't do everything perfectly. The score is calculated by an execution score worth 10 points, and a difficulty score that's unlimited. You get a bigger D-score by doing hard tricks, and you get even more points if you do the hard tricks one after the other, without stopping your movement. But Wieber lost points because she couldn't connect her hard tricks. This combination -- a front handspring, full-twisting back tuck, back handspring -- has given her trouble all year. Here's an earlier competition, where you can see there's not really continuous movement between the tricks: