The life of a single human, as the life of a family or an entire people,
persists as memory. My people must come to see this as part of their maturing
process. They are people as organism, and in this persistent memory they store
more and more experiences in a subliminal reservoir. Humankind hopes to call
upon this material if it is needed for a changing universe. But much that is
stored can be lost in that chance play of accident which we call "fate." Much
may not be integrated into evolutionary relationships, and thus may not be
evaluated and keyed into activity by those ongoing environmental changes which
inflict themselves upon flesh. The species can forget! This is the special
value of the Kwisatz Haderach which the Bene Gesserits never suspected: the
Kwisatz Haderach cannot forget.

-The Book of Leto, After Harq al-Ada