Actual or personal sin is an offense against God. Personal sin, as opposed to Original Sin, is the willful disobedience to God’s will.
This disobedience may be an action, a thought, a desire, or an intention. A sin must be a conscious and deliberate violation of the moral law. Thus, to sin is to actually say “no” to God. We sin when we refuse God’s love and turn down His invitation to give of ourselves to God and to our fellow men. Furthermore, we sin through personal acts of selfishness which cause harm to others or ourselves.