- They're at least breeding the KH for prescient sight. Makes sense that the ability would manifest itself amongst its members.
- They're heavy spice users.
- Prescience is fairly common, i.e. many of the members of Stilgar's tribe have the sight in a rudimentary degree.
On the other hand, for the longest time, I remembered Bene Gesserit truthsay as the art of predicting the future. And it is not, it's the ability to discern if someone is telling the truth. So the 'feeling' I had that the Bene Gesserit were all spice-addicted fortune tellers is obviously wrong. But maybe not entirely.