66 Such persons grievously err in refusing to recognize the inborn weakness of human nature, and the law of which the Apostle speaks, fighting against the law of the mind; and also in ignoring the experience of facts, from which it is clear that, particularly in young people, evil practices are the effect not so much of ignorance of intellect as of weakness of a will exposed to dangerous occasions, and unsupported by the means of grace.
Source: Divini Illius Magistri (Vatican.va)