Alfred Adler, answered from the texts and cited to the page.
To be a human being is to feel inferior. Every one of us begins life as a small, weak, wholly dependent child in a world of larger and more capable others, and no one escapes the feeling of littleness that this leaves. That feeling is not a disease; it is the spur. From the felt minus the whole of life is a movement toward a plus — toward competence, security, significance, a place among others where one need not feel small.1
Compensation is the name of this movement, and it builds everything: the child who stammers becomes the orator, the sickly boy the athlete, the whole of culture is compensation for human weakness before nature. Neurosis is not a different thing from this but a miscarriage of it: an inferiority felt as unbearable, a goal of superiority pitched too high and too private, and a set of "safeguarding" devices — symptoms, hesitations, retreats — by which the person protects his fragile sense of worth by declining the tasks of life while seeming not to decline them.
I do not make sexuality the master motive, as Freud did; I make the striving from below to above, and I find it under every symptom and every character, because it is the shape of a life lived forward from a helpless beginning.2345
In order to prove his ability to cope with life, all the ''arrangements" and neurotic symptoms necessary for the patient come into existence, as an aid in necessity, as an unduly developed coefficient-of-security against the dangers he anticipates and toward whose prevention he has been unceasingly working when, under the influence of his inferiority feeling, he has been constructing his plans for the future.The Practice and Theory of Individual Psychology, pp. 37–38
We shall then always succeed in finding a life-line, deviating from the direct path, which, on account of fear of mistakes and defeat, is searching for safe side-paths. The falsification of his sexual réle results, in consequence of which the neurotic seems to exhibit a tendency toward '' psychical hermaphrodism", which he actually believes himself to possess.The Practice and Theory of Individual Psychology, p. 35
One cannot expect a child to have a correct estimation of himself in any particular situation; one does not expect it of adults! It is precisely here that difficulties grow apace. One child will grow up in a situation so complicated that errors concerning the degree of his inferiority are absolutely unavoidable. Another child will be able better to interpret his situation.Understanding Human Nature, pp. 75–76
The aim to be great, to be strong, to be a man, to be "above" is symbolized in the person of the father, the mother, the teacher, the coach- man, the locomotive engineer, etc., and the con- duct, the attitude, the imitative gestures, the play of children and their wishes, the day dreams and favorite stories, ideas about their future vocation show us that the compensatory tendency is at 35 36 THE NEUROTIC…The Neurotic Constitution
In a similar manner our actions are determined by the content of experiences, which are given birth to and are determined by the guid- ing fiction. Even our judgments concerning the value of things are determined according to the standard of the imaginary goal, not according to "real" feelings or pleasurable sensations.The Neurotic Constitution
Adler's founding idea and his most enduring popular legacy: the "inferiority complex" is one of the few technical terms of depth psychology to become ordinary speech. Its influence is broad — compensation and the striving for competence run through the humanistic and cognitive psychologies — but it draws the standard objection leveled at all the first-generation schools: that it reduces the whole of human motivation to a single master principle, as Freud reduced it to sexuality and Jung enriched it toward the archetypal. Whether "striving from inferiority to superiority" is the key to the psyche or one motive among many, over-generalized into a system, is the live question; the Ansbachers' systematic edition made the mature, socially-embedded version of the doctrine available against the caricature.