For the past two weeks in Sunday School, Rex has used an illustration that I really liked and that's stuck with me. He compared battling sin to playing a video game.
When you're playing a video game, you expect to get killed. Each time, though, you make it a little bit further. You know to dodge a bullet here; you learn to jump 'just so' at this point. Video gamers get good because they have a tolerance for failure -- and we should, too, in our battle against sin.
We fail in one way, but we embrace God's grace, we learn from it, and we are prepared the next time that particular form of temptation attacks us. But we expect to repeat the cycle ... a lot. And little by little, "we, who with unveiled faces all reflect the Lord's glory, are being transformed into his likeness with ever-increasing glory, which comes from the Lord, who is the Spirit" (2 Cor 3:18).