In the first reading today St. John's sets the bar incredibly high when he writes "No one who remains in him sins."
The more I reflected on his statement the more I realize that John here is not saying that the minute you commit a sin you're out, off you go to hell. What he is giving us here is more an instruction for daily living.
How do we avoid sin? "Remain in him." To put it more simply if we keep Christ in our mind always we will not sin. It would be from his point of view effectively impossible to say, "I am keeping Christ in mind, and sinning simultaneously."
Remember, sin requires not just a bad action, but a bad action combined with thought and will. We have to make a choice to sin. St. John is telling us that if we remain in him, if we keep ourselves constantly mindful of his presence then it is possible for us to avoid sin.
We may still make mistakes, we are imperfect creatures; but sin is avoidable.
Several times each day we need to pause and remind ourselves of that presence of God that is always with us, remain in him, don't step out for even a minute and we will find that avoiding sin is less difficult than we think.