This became very important in Martian Dreams, where the evil Raxachk had himself hidden behind an impenetrable crystal barrier in the Dream-World. Raxachk gloated that even if the Avatar should manage to gain access to his hoarded Dreamstuff, using it to create a weapon powerful enough to bypass the barrier would be impossible for the hero, as Raxachk's psychometric powers had already revealed everything that could be known about everything possessed by the humans on Mars.