"The basic point- which can also be illustrated by considering the phenomenon of the blind spot- is that with any incomplete perception- and needless to say all perceptions are incomplete- the observer "fills in" by extrapolating from experience. Or from desire. Or from desire's other face, aversion. So basically, we focus fuzzy images by transforming them into what we expect to see, or what we most dread to see. By what, in other words, already exists in our mind, what we already have available on file, however dusty the folder."
from Atmospheric Disturbances by Rivka Galchen