Losing focus is the path to sin

Since therefore Christ suffered in the flesh, arm yourselves with the same way of thinking, for whoever has suffered in the flesh has ceased from sin, so as to live for the rest of the time in the flesh no longer for human passions but for the will of God. (1 Peter 4:1, 2 ESV)

When we turn fom the world towards Christ, our purpose and passion goes from seeking pleasure in the things of the flesh to seeking the will of God.  It's not that we won't sin, it's that now our purpose and passion is no longer motivated by it.  We are instead motivated by God and the direction that He provides every minute of everyday.  When that is our purpose and passion, sin comes around when we lose focus.