Is it impossible for a finite human to commit a mortal sin by its very definition?

A mortal sin requires 3 things: grave matter, full knowledge, and deliberate consent. As finite beings, we cannot fully know God--this is stated by the apophatic tradition which includes Aquinas and Dionysus the Areopagite. Thus, we cannot know with absolute certainty what God considers a grave matter. The Catholic Church has not put together an infallible list of grave matters. Even if we were sure that God considered something a grave matter, we could not be absolutely sure that any specific act is an example of that grave matter. Stabbing someone in one instance is murder; in another, it is surgery. Is sex with a concubine adultery? We cannot know all the subconscious drives or instincts which contribute to any of our decisions. We are not in absolute control of our actions. Much of our choice is based on unconscious survival instincts of which we are not aware inherited from our ancestors. Untreated PTSD can trigger violent acts. We don't know how much systemic or cultural forces are contributing to our choice. For instance, stealing drugs when there is no national program to reduce prices might be a mitigating factor. I might not be aware of my racism because I'm living in a racist community. We can't overcome our limited knowledge of God. We can't fully know the nature of any specific act. Psychology and social science show we are not in full control of any of our decisions. No amount of deliberation can overcome unconscious or cultural forces. We cannot, of our own will, overcome concupiscence. Therefore, finite beings cannot fulfill the conditions for mortal sin. Right?