The similarities as regards _general or special circumstances_ may also on occasion be important in determining the direction of transference and in cases where the process of displacement has suffered an arrest at a comparatively early stage, may cause serious difficulties or restrictions in the choice of object. [Sidenote: Falling in love with those who are already married or betrothed] Thus it may happen that, just as the child's love activities in relation to its earliest love object were impeded by the fact that this object was already bound by affection, law or both, to a third person (_i. e._ the parent of the same sex as that of the child), so in adult life the individual's choice may fall only on objects who are similarly not at liberty in the disposal of their affections[120]. There are indeed some men and women who can only fall in love with married or betrothed persons, and who are doomed therefore either to become dangerous enemies to the harmonious married life of others or else themselves to suffer successive repetitions of the unsuccessful love of their childhood[121]. Marriage in such cases may bring no relief, because the object of their affection may cease to exercise attraction as soon as its possession is undisputed and unhindered. The widespread occurrence and intensity of the unconscious ideas underlying this kind of aberration is shown by the frequent treatment of the subject in legend and literature (_Cp._ Tristan and Iseult, Paolo and Francesca, Pelleas and Melisande, Don Carlos and his step-mother, Casandra and a host of other examples in which the expression and fulfilment of a great love are prevented by the fact that one of the lovers is already married or affianced to a third person, usually a relative, and one who on analysis can easily be shown to represent the parent who stood in the way of the first love of the child.)[122]. [Sidenote: The desire for obstacles in the way of love] In a number of other cases stress is laid not so much on the unfree condition of the loved object, but, more generally, on the barrier raised by the incestuous nature of the desired relationship. This factor will of course in the majority of cases merely add its force to those demanding previous marriage or betrothal to another as a necessary qualification of the loved object, but will sometimes manifest itself alone as a felt _need for_ the occurrence of some sort of _hindrance_ to the consummation of love, the lover being unable to derive full satisfaction from the union or to remain permanently attracted to his chosen object in the absence of such hindrance[123]. Here it will usually be found that the loved object is unconsciously identified with the parent or with some other near relation.