Alfred Adler, answered from the texts and cited to the page.
A human life cannot be understood by asking only where it came from; you must ask where it is going.1 The person is not merely pushed from behind by his past — by his drives, his traumas, his heredity — as a stone is pushed by the hand that throws it. He is pulled from in front by a goal: an image, formed in early childhood and mostly unknown to him, of what he would have to be and have in order to feel secure and significant.
This goal is a "fiction" — it need not be true or attainable; it works by being lived toward, as if it were the point of everything. Grasp a person's goal and the whole apparent chaos of his conduct arranges itself: the symptom, the memory he keeps, the way he enters a room, all serve the single guiding purpose, and what looked like contradiction is revealed as a consistent movement toward one end.
This is the teleological method, and it is why I can read a life from its parts — a childhood recollection, a posture, a first dream — because each part expresses the whole style of life that the goal unifies.2 Causes constrain; goals direct; and it is the direction that makes a person who he is.
And in order to understand a person's future we must understand his style of life. Even if we understand instincts, stimuli, drive, etc., we cannot predict what must happen. 99 THE SCIENCE OF LIVING Some psychologists indeed try to reach conclu- sions by noting certain instincts, impressions or traumas, but on closer examination it will be found that all these elements presuppose a con- sistent style of life.The Science of Living
If we reaffirm what has been said concerning the teleology of the psychic Life of mankind it will become increasingly clear to us that an indestructible unity must be a special token of this behavior pattern. The necessity for treating with a human being only as unit personality becomes increasingly clear in those cases where seemingly contrasting expressions of psychic trends are to be found.Understanding Human Nature, p. 82
One of Adler's most distinctive and most philosophically freighted commitments, drawn explicitly from Vaihinger's fictionalist philosophy, and the sharpest point of his divergence from Freud's causal-deterministic model. It placed him on the teleological side of the long quarrel in psychology between explanation by causes and explanation by purposes. The teleological method — reading the whole life from a part as an expression of the guiding goal — became the working core of Adlerian assessment. Critics charge that teleology is either unscientific (final causes have no place in a natural science) or empty (a goal can be inferred to fit any conduct after the fact). Later psychology largely kept the substance under other names — the study of goals, expectancies, and self-set standards — while shedding the fictionalist metaphysics.