Danito- You nailed my perspective. The insight and "master-planning" that went into the creation of Don Vito's empire did not overlook the structure of his own organization. In fact, though he spent spent so much time in doing so, he made the single greatest mistake of his life in making Hagen consigliere. Point is, though he made a key error in judgement, he did not overlook the nuance of examining and planning the internal structure. This combined with Michael's discarding of Fredo- which I believe happened long before Michael's "you're nothing to me now" line opened the possibility of betrayel at the highest and closest level.