Michael's Deductions on Hyman Roth.
I've never quite understood how Michael figured out it was Hyman Roth behind his attempted assaination. Was it in the process of Michael feeling out Roth and witnessing his anger over the Moe Green hit? As well as realising that Fredo was lying about never having meet Johnny Ola?
Even so, how does Michael pick up on Roth's belief that he's going to live forever when Roth had repeatedly lamented his inpending death? And what was Roth's end game? He tried to kill Michael but he still needed his investment in Havana? Can't work that one out.
The trilogy seems to have a thing for unexplained deductions made by the characters. Witness Vito in the first film coming to the conclusion out of thin air that Barzini had Sonny killed.