quote from Turnbull:
He said it all when he told Michael, "I don't have your head for the big deals...but why don't we hit 'em now, while we have the muscle?" He used the Roman analogy ...
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I don't understand why Frankie underestimated Michael's balls. I don't think anybody should underestimate a man who order the killing of the Head of the Five Families.
To me Michael is still the Emperor of his Romans.
So I guess this two gays just wasn't made for each other. Frankie with his simplicity, and Michael with his intelligence (tactical), yet cold and ruthless.
If only Frankie were still alive in GF III, he will see what kind of empire Michael had built (getting stronger and more influence ... from Vaticans ...), before Michael's guilt (Fredo's killing etc) getting unbearable, and his determined to go legitimate (finally).