Shot: A subject may know full well the rule, yet have great difficulty in understanding “its inherent values”, or be in a concrete situation which does not allow him or her to act differently and decide otherwise without further sin. Amoris Laetitiae, §301 Chaser: If anyone says that the commandments of God are impossible to observe even for a man who is justified and established in grace, let him be anathema.

The existence of God can be proven/demonstrated from reason alone. But don’t take my word for it: Oath Against Modernism (Denz. 2145) And first, I profess that God, the beginning and end of all things, can be certainly known and thus can also be demonstrated by the natural light of reason “by the things that are made” [cf. Romans 1:20], that is, by the visible works of creation, as the cause by the effects.