"Let us imagine [writes Freud][11] an undifferentiated vesicle of
sensitive substance: then its surface, exposed as it is to the
outer world, is by its very position differentiated, and serves as
an organ for receiving stimuli.... This morsel of living substance
floats about in an outer world which is charged with the most
potent energies, and it would be destroyed ... if it were not
furnished with protection against stimulation. [On the other hand]
the sensitive cortical layer has no protective barrier against
excitations emanating from within.... The most prolific sources of
such excitations are the so-called instincts of the organism....
The child never gets tired of demanding the repetition of a game
... he wants always to hear the same story instead of a new one,
insists inexorably on exact repetition, and corrects each deviation
which the narrator lets slip by mistake.... According to this, _an
instinct would be a tendency in living organic matter impelling it
towards reinstatement of an earlier condition_, one which it had
abandoned under the influence of external disturbing forces--a kind
of organic elasticity, or, to put it another way, the manifestation
of inertia in organic life.

"If, then, all organic instincts are conservative, historically
acquired, and directed towards regression, towards reinstatement of
something earlier, we are obliged to place all the results of
organic development to the credit of external, disturbing, and
distracting influences. The rudimentary creature would from its
very beginning not have wanted to change, would, if circumstances
had remained the same, have always merely repeated the same course
of existence.... It would be counter to the conservative nature of
instinct if the goal of life were a state never hitherto reached.
It must be rather an ancient starting point, which the living being