A loss in the first week of the season is not fatal. If you come out of that first week with a laundry list of things you can fix and you do fix them, the rest of the season can proceed quite merrily. See the 2016 Falcons, who rattled off four wins following their Week 1 loss and went on to the Super Bowl.
Then there are the Week 1 losses that are a harbinger of things to come. The 2019 Falcons won their Week 2 matchup against the Eagles after a crushing loss to the Vikings in Week 1, but then would lose six straight games and the season was dead at the halfway mark.