Is a season made in one week in the NFL? No. Two? Probably not, but things do start to get complicated. For the Seattle Seahawks, starting the season 0-2 could be grave. The NFC West is no joke.
That is the difference between, say, the Seahawks and the Atlanta Falcons. Seattle is better than Atlanta, but the Falcons play in a much easier division. They could fall to 0-3, and things might be OK. If the Seahawks do that, the season could be done.
The San Francisco 49ers, Los Angeles Rams, and (maybe) the Arizona Cardinals are all good teams and could all end up with winning records.