Yup. It happens to everyone. Only two teams have ever gotten through the regular season undefeated.
There'll be a game where the opponent hits on a big play here and falls on a fumble there and hangs around until the 4th quarter and manages to squeak by with a close win. That's how good teams lose to lesser teams, it happens to all of them at some point, and it shouldn't change your opinion of the team very much.
When you start getting blown out in games? That's when you know you're not very good.