A little idea about the choice

Well, then the world of choice is an interesting world. And I have a question: About a year ago, I remember myself in Genesis lessons, studying Genesis 4 about the story of Cain and Abel. The rabbi gives an interpretation according to which the older brother automatically gives in to his brother because he takes away his status as a 'son' and turns him into a 'brother' and we study the verses. Now, we come to verse 5: And Cain was very angry, and his face fell. – The rabbi asks us, what happened to Cain? And he immediately answers that it is a double consequence. On the one hand, nervousness, and on the other hand, an expression expressing shame, "and his face fell." On the one hand, the nervousness is understandable: you are rejected before God. But why did Cain fall into depression? And the rabbi immediately answers: Because Cain thought that he had no ability to change. That his fate was sealed. And immediately continues reading the verses: 6 And the Lord said to Cain, "Why are you angry? Why is your countenance downcast? 7 If you do well, and if you do not do well, sin will come to you, and you will bring it to me, and you will rule over it." – The Lord revealed to Cain that he had a choice! That he could rule over sin! I remember myself in class not understanding why we waste half an hour on this explanation. What is this nonsense?

Until I saw the video a while ago –
http://www.youtube.com/watch?v=V0YwNEKtRCc&ab_channel=ShalemCollege-ShalemAcademicCenter
And I said to myself, wow, there is indeed something difficult here. Do you think there is any weight to the fact that a person actually feels that he has a choice throughout his life? Does this indicate anything?