... back two steps: Michael's real weakness that his obsession with becoming "legitimate" by acquiring Roth's Havana empire blinded him to Roth's treachery--which included recruiting his own brother for betrayal.
Fabulous point, Turnbull. Nail on the head!!!
(Little wonder he wanted Roth dead even after he had 'won'!)
As for Michael's oversight of the possibility of Fredo's simplicity leading to Fredo's being passed over leading to Fredo's resentment leading to Fredo's betrayal....I suppose in hindsight that's a pretty neat package all tied up with pink ribbon. But...even the ingenious Michael Corleone was likely incapable of entertaining such a course of events and therefore keeping his brother under a 'watchful eye'.
