What I don't get is how Michael and somewhat the great Don himself - Vito basically left Fredo behind and almost letting him know that he is worthless... Maybe not Vito but certainly Michael did by having him be some personal driver. At least Mike revealed to him in II who his enemy was.

Why didn't Vito set him up with a more important role? Maybe let him take part in the legitimate business in the olive oil company after Genco passed and even have him eventually fully incharge of the egit businesses. We don't even get to know enough about him in the first film to label him a moron as most seem to. Just because you're not cut out for the life and happen to drop a handgun on the ground on the first day driving the Don after work as bullets quite nearly striking yourself doesn't make you an idiot lol. Fredo was young still and can't have been a hopeless case.

Vito and Michael, leaders of the most powerful crime organisation but couldn't figure out or bother enough with the consequences to follow.