There are several reasons, any one of which had been different, we probably would have won:
1. If we'd had a strong base pass rush.
2. If Shawn hadn't fumbled. Pretty sure Atlanta's choke job starts half a game early if not for that.
3. If Clemons wasn't hurt. Unexpectedly allowing Atlanta so many rushing yards REALLY hurt.
4. If we hadn't blitzed. We didn't blitz all year and relied on our all world secondary. QBs hear a ticking in their ear whether there's a good rush or not. Ryan likes to get the ball out of his hands fast. We've done a great job all year with little pressure. After the first pick by Ryan on a blitz, he absolutely shredded us on blitzes, including the last drive. Even though it was a popular sentiment around here, I expected Seattle to ignore the pressure and stick to its guns. Unfortunately, they didn't, and it's one decision that cost the game.
5. If we'd played press man coverage on the final drive. We'd gotten Atlanta off the field on two previous critical drive but reverted to the "safe", but in reality most risky, soft zone coverage on the last drive. Brock Huard broke down the first play of that drive and mentioned that, as a QB, he always preferred to see the soft zone over the press man because it gave him lots of space to throw into.
6. This is the weakest point by far, in my opinion, but the drive to end the first half could have been handled better. It's hard to say a field goal at that point is critical, though, so I'm not sure the call to go for it was wrong. The play call was poor in my opinion. After seeing the defense, I think Wilson should have checked out of it or something. I think it was pretty awful to call it twice in a row. At the ends of seasons, at critical points against really good teams, it doesn't pay to be predictable, no matter how many times that play had been called in the past. As Atlanta later said, they'd seen that play in film. We had no momentum at that point, playing on the road, Atlanta's defense amped up...I feel like everyone here must have known what was coming and that it would be stopped. Hindsight is 20/20, yeah, yeah, but sometimes stuff really is too predictable. Atlanta was absolutely primed to stop that play. A counter for their aggression would have been the perfect call. Also, you should already be using non-voice signals to communicate plays by then. Nor do I like how casual those end of first half drives have been lately. Anyway, although I've devoted the most space to this point, it's the least important.