Now your impression will be that abstinence has become an insignificant factor, since there are so many methods of enduring it. Yet this is not the case, for its pathological power is unimpaired. The remedies are generally not sufficient. The measure of unsatisfied libido which the average human being can stand is limited. The plasticity and freedom of movement of libido is by no means retained to the same extent by all individuals; sublimation can, moreover, never account for more than a certain small fraction of the libido, and finally most people possess the capacity for sublimation only to a very slight degree. The most important of these limitations clearly lies in the adaptability of the libido, as it renders the gratification of the individual dependent upon the attainment of only a very few aims and objects. Kindly recall that incomplete development of the libido leaves extensive and possibly even numerous libido fixations in earlier developmental phases of the processes of sexual organization and object-finding, and that these phases are usually not capable of affording a real gratification. You will then recognize libido fixation as the second powerful factor which together with abstinence constitutes the causative factors of the illness. We may abbreviate schematically and say that libido fixation represents the internal disposing factor, abstinence the accidental external factor of the etiology of neurosis. I seize the opportunity to warn you of taking sides in a most unnecessary conflict. In scientific affairs it is a popular proceeding to emphasize a part of the truth in place of the whole truth and to combat all the rest, which has lost none of its verity, in the name of that fraction. In this way various factions have already separated out from the movement of psychoanalysis; one faction recognizes only the egoistic impulses and denies the sexual, another appreciates the influence of objective tasks in life, but ignores the part played by the individual past, and so on. Here is occasion for a similar antithesis and subject for dispute: are neuroses _exogenous_ or _endogenous_ diseases, are they the inevitable results of a special constitution or the product of certain harmful (traumatic) impressions; in particular, are they called forth by libido fixation (and the sexual constitution which goes with this) or through the pressure of forbearance? This dilemma seems to me no whit wiser than another I could present to you: is the child created through the generation of the father or the conception of the mother? Both factors are equally essential, you will answer very properly. The conditions which cause neuroses are very similar if not precisely the same. For the consideration of the causes of neuroses, we may arrange neurotic diseases in a series, in which two factors, sexual constitution and experience, or, if you wish, libido-fixation and self-denial, are represented in such a way that one increases as the other decreases.