The schedule gets tougher after the bye week
Speaking of the schedule, Seattle started the season by going through one of their "easier" stretches. While they lost badly to the Rams, they got a good win in Week 2 with a victory over the Lions. The combined record of the first four teams Seattle played is currently 6-10 with the Giants and Panthers being a combined 1-7.
After Week 7 (and that stretch includes a still-dangerous Bengals team), Seattle will start a stretch of 10 games facing teams that do not currently have a losing record. Seattle is capable of winning a majority of those games, of course, but only if they play well and consistently. Seattle cannot have too many games where they are good for entire halves. Seattle was bad in the second half of Week 1 against the Rams and then weren't great offensively in the first half of Week 2 against the Lions and then in the first half of Week 3, Seattle could only kick field goals.
The Seahawks need to start consistently putting whole games together or any team they play can beat them the rest of the season. While the Arizona Cardinals are going to have a losing record and don't have as much talent as Seattle, they clearly play hard for their new coaching staff and they have already beaten the Dallas Cowboys this year. On any given Sunday...
My point in this is not to say that Seattle's promising season is about to end with the team having a losing record, but there are two ways of looking at this. One is that Seattle could struggle to get to 9 wins and miss the playoffs if they don't play well offensive and defensively nearly every week. The other is that Seattle is going to win 12 games and be hardened by the time the playoffs arrive and be a very dangerous postseason team.