The Home Life of Cain and Able

I have given much thought to Cain and Abel recently. Particularly, their family dynamic and ultimate salvation. While Cain may not have been fathered by Adam, Adam certainly raised him, just the same as Able. Both boys grew up in the same household, and likely received the same opportunities, yet chose two very different paths. 
Would God not have forgiven Cain at any time? Would God not have accepted Cain if he chose to humble himself before God? Of course God would have. However, Cain still  chose the path he did and chose to sin wickedly against his brother. I just find this interesting and it provides a perfect Biblical example of how everyday choices shape our future. Our environment can only shape us to a point, ultimately it is up to us to choose.