In socionics, the dual-seeking function is more of a "pseudo-function"; a fake strength. You use your 5th function, but when you do, it is a more twisted form of the pure function. The 5th funciton exists because of repression of the 3rd function. After you try and push your 3rd function down (by the 1st), your 5th function is naturally created, subconciousley.
For example, Si. In Si dominant types, you can see that they have Ne, but it is a more dark form of it. Si dominant types have intuitions, but they aren't really "true" intuitions like the Ne dominant types, because the Si types can start to invision the worst possible scenarios when something happens. This happens in a case where they were waiting to meet someone, but that person happens to be late. They will start to think that the person might have gotten into an accident, or robbed, or some other silly thing that is actually detached from what you would normally percieve to happen. Jung mentioned how these "dual-seeking" functions manifest themselves (although he didn't call them that). Here they are:
His unconscious is distinguished chiefly by the repression of intuition, which thereby acquires an extraverted and archaic character. Whereas true extraverted intuition has a characteristic resourcefulness, and a 'good nose' for every possibility in objective reality, this archaic, extraverted intuition has an amazing flair for every ambiguous, gloomy, dirty, and dangerous possibility in the background of reality. In the presence of this intuition the real and conscious intention of the object has no significance; it will peer behind every possible archaic antecedent of such an intention. It possesses, therefore, something dangerous, something actually undermining, which often stands in most vivid contrast to the gentle benevolence of consciousness. So long as the individual is not too aloof from the object, the unconscious intuition effects a wholesome compensation to the rather fantastic and over credulous attitude of consciousness. But as soon as the unconscious becomes antagonistic to consciousness, such intuitions come to the surface and expand their nefarious influence: they force themselves compellingly upon the individual, releasing compulsive ideas about objects of the most perverse kind. The neurosis arising from this sequence of events is usually a compulsion neurosis, in which the hysterical characters recede and are obscured by symptoms of exhaustion. [p. 505]
The introverted intuitive's chief repression falls upon the sensation of the object. His unconscious is characterized by this fact. For we find in his unconscious a compensatory extraverted sensation function of an archaic character. The unconscious personality may, therefore, best be described as an extraverted sensation-type of a rather low and primitive order. Impulsiveness and unrestraint are the characters of this sensation, combined with an extraordinary dependence upon the sense impression. This latter quality is a compensation to the thin upper air of the conscious attitude, giving it a certain weight, so that complete 'sublimation' is prevented. But if, through a forced exaggeration of the conscious attitude, a complete subordination to the inner perception should develop, the unconscious becomes an opposition, giving rise to compulsive sensations whose excessive dependence upon the object is in frank conflict with the conscious attitude. The form of neurosis is a compulsion-neurosis, exhibiting symptoms that are partly hypochondriacal manifestations, partly hypersensibility of the sense organs and partly compulsive ties to definite persons or other objects. [p. 511]
So long as the ego feels itself housed, as it were, beneath the heights of the unconscious subject, and feeling reveals something higher and mightier than the ego, the type is normal. The unconscious thinking is certainly archaic, yet its reductions may prove extremely helpful in compensating the occasional inclinations to exalt the ego into the subject. But, whenever this does take place by dint of complete suppression of the unconscious reductive thinking-products, the unconscious thinking goes over into opposition and becomes projected into objects. Whereupon the now egocentric subject comes to feel the power and importance of the depreciated object. Consciousness begins to feel 'what others think'. Naturally, others are thinking, all sorts of baseness, scheming evil, and contriving all sorts of plots, secret intrigues, etc. To prevent this, the subject must also begin to carry out preventive intrigues, to suspect and sound others, to make subtle combinations. Assailed by rumours, he must make convulsive efforts to convert, if possible, a threatened inferiority into a superiority. Innumerable secret rivalries develop, and in these embittered struggles not only will no base or evil means be disdained, but even virtues will be misused and tampered with in order to play the trump card. Such a development must lead to exhaustion. The form of neurosis is neurasthenic rather than hysterical; in the case of women we often find severe collateral physical states, as for instance anæmia and its sequelæ.
The thinking of the introverted type is positive and synthetic in the development of those ideas which in ever increasing measure approach the eternal validity of the primordial images. But, when their connection with objective experience begins to fade, they become mythological and untrue for the present situation. Hence this thinking holds value only for its contemporaries, just so long as it also stands in visible and understandable connection with the known facts of the time. But, when thinking becomes mythological, its irrelevancy grows until finally it gets lost in itself. The relatively unconscious functions of feeling, intuition, and sensation, which counterbalance introverted thinking, are inferior in quality and have a primitive, extraverted character, to which all the troublesome objective influences this type is subject to must be ascribed. The various measures of self-defence, the curious protective obstacles with which such people are wont to surround themselves, are sufficiently familiar, and I may, therefore, spare myself a description of them. They all serve as a defence against 'magical' influences; a vague dread of the other sex also belongs to this category.
This attitude has immense dangers -- all too easily the intuitive may squander his life. He spends himself animating men and things, spreading around him an abundance of life -- a life, however, which others live, not he. Were he able to rest with the actual thing, he would gather the fruit of his labours; yet all too soon must he be running after some fresh possibility, quitting his newly planted field, while others reap the harvest. In the end he goes empty away. But when the intuitive lets things reach such a pitch, he also has the unconscious against him. The unconscious of the intuitive has a certain similarity with that of the sensation-type. Thinking and feeling, being relatively repressed, produce infantile and archaic thoughts and feelings in the unconscious, which may be compared [p. 467] with those of the countertype. They likewise come to the surface in the form of intensive projections, and are just as absurd as those of the sensation-type, only to my mind they lack the other's mystical character; they are chiefly concerned with quasi-actual things, in the nature of sexual, financial, and other hazards, as, for instance, suspicions of approaching illness. This difference appears to be due to a repression of the sensations of actual things. These latter usually command attention in the shape of a sudden entanglement with a most unsuitable woman, or, in the case of a woman, with a thoroughly unsuitable man; and this is simply the result of their unwitting contact with the sphere of archaic sensations. But its consequence is an unconsciously compelling tie to an object of incontestable futility. Such an event is already a compulsive symptom, which is also thoroughly characteristic of this type. In common with the sensation-type, he claims a similar freedom and exemption from all restraint, since he suffers no submission of his decisions to rational judgment, relying entirely upon the perception of chance, possibilities. He rids himself of the restrictions of reason, only to fall a victim to unconscious neurotic compulsions in the form of oversubtle, negative reasoning, hair-splitting dialectics, and a compulsive tie to the sensation of the object. His conscious attitude, both to the sensation and the sensed object, is one of sovereign superiority and disregard. Not that he means to be inconsiderate or superior -- he simply does not see the object that everyone else sees; his oblivion is similar to that of the sensation-type -- only, with the latter, the soul of the object is missed. For this oblivion the object sooner or later takes revenge in the form of hypochondriacal, compulsive ideas, phobias, and every imaginable kind of absurd bodily sensation. [p. 468]
The specially compulsive character of the neurotic symptoms represent the unconscious counterweight to the laisser aller morality of a purely sensational attitude, which, from the standpoint of rational judgment, accepts without discrimination, everything that happens. Although this lack of basic principles in the sensation-type does not argue an absolute lawlessness and lack of restraint, it at least deprives him of the quite essential restraining power of judgment. Rational judgment represents a conscious coercion, which the rational type appears to impose upon himself of his own free will. This compulsion overtakes the sensation-type from the unconscious. Moreover, the rational type's link to the object, from the very existence of a judgment, never means such an unconditioned relation as that which the sensation-type has with the object. When his attitude reaches an abnormal one-sidedness, he is in danger of falling just as deeply into the arms of the unconscious as he consciously clings to the object. When he becomes neurotic, he is much harder to treat in the rational way, because the functions to which the physician must appeal are in a relatively undifferentiated state; hence little or no trust can be placed in them. Special means of bringing emotional pressure to bear are often needed to make him at all conscious.
So long as conscious feeling preserves the personal character, or, in other words, so long as the personality does not become swallowed up by successive states of feeling, this unconscious thinking remains compensatory. But as soon as the personality is dissociated, becoming dispersed in mutually contradictory states of feeling, the identity of the ego is lost, and the subject becomes unconscious. But, because of the subject's lapse into the unconscious, it becomes associated with the unconscious thinking -- function, therewith assisting the unconscious [p. 452] thought to occasional consciousness. The stronger the conscious feeling relation, and therefore, the more 'depersonalized,' it becomes, the stronger grows the unconscious opposition. This reveals itself in the fact that unconscious ideas centre round just the most valued objects, which are thus pitilessly stripped of their value. That thinking which always thinks in the 'nothing but' style is in its right place here, since it destroys the ascendancy of the feeling that is chained to the object.
Unconscious thought reaches the surface in the form of irruptions, often of an obsessing nature, the general character of which is always negative and depreciatory. Women of this type have moments when the most hideous thoughts fasten upon the very objects most valued by their feelings. This negative thinking avails itself of every infantile prejudice or parallel that is calculated to breed doubt in the feeling-value, and it tows every primitive instinct along with it, in the effort to make 'a nothing but' interpretation of the feeling. At this point, it is perhaps in the nature of a side-remark to observe that the collective unconscious, i.e. the totality of the primordial images, also becomes enlisted in the same manner, and from the elaboration and development of these images there dawns the possibility of a regeneration of the attitude upon another basis.
The destructive quality of this thinking as well as its occasional and limited usefulness, hardly need further elucidation. But there still exists another form of negative thinking, which at first glance perhaps would scarcely be recognized as such I refer to the theosophical thinking which is to-day rapidly spreading in every quarter of the globe, presumably as a reaction phenomenon to the materialism of the epoch now receding. Theosophical thinking has an air that is not in the least reductive, since it exalts everything to transcendental and world-embracing ideas. A dream, for instance, is no [p. 445] longer a modest dream, but an experience upon 'another plane'. The hitherto inexplicable fact of telepathy is ,very simply explained by 'vibrations' which pass from one man to another. An ordinary nervous trouble is quite simply accounted for by the fact that something has collided with the astral body. Certain anthropological peculiarities of the dwellers on the Atlantic seaboard are easily explained by the submerging of Atlantis, and so on. We have merely to open a theosophical book to be overwhelmed by the realization that everything is already explained, and that 'spiritual science' has left no enigmas of life unsolved. But, fundamentally, this sort of thinking is just as negative as materialistic thinking. When the latter conceives psychology as chemical changes taking place in the cell-ganglia, or as the extrusion and withdrawal of cell-processes, or as an internal secretion, in essence this is just as superstitious as theosophy. The only difference lies in the fact that materialism reduces all phenomena to our current physiological notions, while theosophy brings everything into the concepts of Indian metaphysics. When we trace the dream to an overloaded stomach, the dream is not thereby explained, and when we explain telepathy as 'vibrations', we have said just as little. Since, what are 'vibrations'? Not only are both methods of explanation quite impotent -- they are actually destructive, because by interposing their seeming explanations they withdraw interest from the problem, diverting it in the former case to the stomach, and in the latter to imaginary vibrations, thus preventing any serious investigation of the problem. Either kind of thinking is both sterile and sterilizing. Their negative quality consists in this it is a method of thought that is indescribably cheap there is a real poverty of productive and creative energy. It is a thinking taken in tow by other functions. [p. 446]