By virtue of the principle of pain the first system is therefore altogether incapable of introducing anything unpleasant into the mental associations. The system cannot do anything but wish. If this remained so the mental activity of the second system, which should have at its disposal all the memories stored up by experiences, would be hindered. But two ways are now opened: the work of the second system either frees itself completely from the principle of pain and continues its course, paying no heed to the painful reminiscence, or it contrives to occupy the painful memory in such a manner as to preclude the liberation of pain. We may reject the first possibility, as the principle of pain also manifests itself as a regulator for the emotional discharge of the second system; we are, therefore, directed to the second possibility, namely, that this system occupies a reminiscence in such a manner as to inhibit its discharge and hence, also, to inhibit the discharge comparable to a motor innervation for the development of pain. Thus from two starting points we are led to the hypothesis that occupation through the second system is at the same time an inhibition for the emotional discharge, viz. from a consideration of the principle of pain and from the principle of the smallest expenditure of innervation. Let us, however, keep to the fact--this is the key to the theory of repression--that the second system is capable of occupying an idea only when it is in position to check the development of pain emanating from it. Whatever withdraws itself from this inhibition also remains inaccessible for the second system and would soon be abandoned by virtue of the principle of pain. The inhibition of pain, however, need not be complete; it must be permitted to begin, as it indicates to the second system the nature of the memory and possibly its defective adaptation for the purpose sought by the mind.