Vito Corleone had 3 facets highlighted in the film:
- He had high testosterone/ Highly masculine,
- He was very emotional about family, emphatic, understanding, and generally tender-hearted.
- He was Machiavellian; Calculated.
Each part of him enhanced the other two, and all 3 parts coalesced to bring us the balanced Vito we know and love.
The thing is, When he gave birth to his sons, each son got just one of those character traits, without the other two to balance it out:
- Brash masculinity went to Santino
- Soft heartedness went to Fredo
- Machaivellian nature went to Michael.
Here's an example of the Fredo in him.
Here's what Michael got:
Lemme highlight the hot temper that he passed down to sonny.
In the very beginning of the film, when Amerigo Bonasera — the funeral parlour owner seeking revenge for the disfiguring of his daughter — is weeping as he tells his story, when he walks away from whispering that he wants the culprits dead, you can see the disgust in Vito Corleone's face. That's suppressed emotion. He wants to spaz out on Bonasera for being a p*ssy, but he can't, cause sonny's in the room. But that reasoning isn't revealed immediately...
You see his general feelings for Bonasera again right after he's left the room.
Later on during the Wedding celebration, Johnny Fontaine, A singer and one of Vito's Godsons, is expressing a problem in the same home office that Bonasera and all the others made requests in. He's crying cause he fell off and he's being rejected for a part in a movie that would bring him back to prominence. This time Santino isn't in the room, so Vito cuts loose:
right as he's going in on Johnny, Santino walks in. Soon as Vito notices that, he Switches back to stoic Godfather mode. That's when he hits Johnny with the "you spend time with your family? Good, cause a man that doesn't spend time with his family can never be a real man."
That classic quote is actually an in-the-moment improvisation. See he knows that Sonny got his hot temper from him, so he hides it whenever Sonny's around, for fear that Sonny would feel validated in that behavior, and become worse.
And that's where he fukked up.
If he woulda noticed the traits that his kids lacked early on in life, and, instead of fukkin hiding his traits, Gave his kids knowledge of self, explained where those character traits came from, and instilled specific values in each individual son to rectify those imbalances, Each son would've made better judgement calls, and all the errors they made would have been avoided.
- Sonny's L came from errors of him being too hotheaded.
- Fredo's L came from errors of him being too tenderhearted.
- Michael's L came from errors of him being too Machiavellian.
All three traits came from Don Vito.
And since he's their father and he failed to spot those character imbalances and make early efforts to correct them, All their failures fall squarely on him.