As a defensive player in soccer, I often hear the phrase: "When in doubt, kick it out." In soccer, if you mess around with the ball in the back, it can result in a point for the opposing team. And that is bad! So, when a ball comes to those of us on defense and we are unsure whether or not we have time to pass it, we kick it out.
In life, we sometimes have things that we think might be impure, but we are not really sure, so we keep them in our lives. Keeping impure things in our lives, however, separates us from God and hurts our witness.