I disagree and would love to hear this discussed. From the moment the Don is shot I think we can 'visibly' on screen see his character adjusting to the role that he will later take. Mike makes up his mind almost immediately in the hospital scene that he will risk his life to defend his father/family just like he did for his country.

When Santino dies, his fate is sealed. I love watching the look on his face when learning of his brother's death. Is he mourning and shocked b/c of the death of Sonny? Or is it the death of his 'old self'. I think that's one of the reasons he snatches Kay up, to get a grasp on that past that will never be.

If he 'completely lets go' what in the world may become of his mother, brother, and sister etc??? Probably DANGEROUS and maybe impossible to get out.