to sleep is quite compatible with the retention of a certain amount of
attention in a given direction.

But we must here take cognizance of an objection that is based on a
better knowledge of the unconscious processes. Although we have
ourselves described the unconscious wishes as always active, we have,
nevertheless, asserted that they are not sufficiently strong during the
day to make themselves perceptible. But when we sleep, and the
unconscious wish has shown its power to form a dream, and with it to
awaken the foreconscious, why, then, does this power become exhausted
after the dream has been taken cognizance of? Would it not seem more
probable that the dream should continually renew itself, like the
troublesome fly which, when driven away, takes pleasure in returning
again and again? What justifies our assertion that the dream removes the
disturbance of sleep?

That the unconscious wishes always remain active is quite true. They
represent paths which are passable whenever a sum of excitement makes
use of them. Moreover, a remarkable peculiarity of the unconscious
processes is the fact that they remain indestructible. Nothing can be
brought to an end in the unconscious; nothing can cease or be forgotten.
This impression is most strongly gained in the study of the neuroses,
especially of hysteria. The unconscious stream of thought which leads to
the discharge through an attack becomes passable again as soon as there
is an accumulation of a sufficient amount of excitement. The
mortification brought on thirty years ago, after having gained access to
the unconscious affective source, operates during all these thirty years
like a recent one. Whenever its memory is touched, it is revived and
shows itself to be supplied with the excitement which is discharged in
a motor attack. It is just here that the office of psychotherapy begins,