Leto turning into a worm is kind of a culmination of the whole Kwisatz Haderach idea. Jessica screwed up when she bore Paul a generation too early, which screwed up the projections and centuries old plans of the Bene Gesserit for their Shortening of the Way. Leto was the culmination of that failure of the Bene Gesserit. Ironically, the biggest failure in the eyes of the Bene Gesserit is the biggest hope humanity could get ( ... )