An intense psychological association with a past event or series of events that triggers certain feelings or behaviors in a person when confronted with similar events or series of events.
Sigmund Freud theorized that the developmental stages of infancy and early childhood chart our lives in ways that are difficult to change. He believed that most adult neuroses could be attributed to a fixation developed during one of these stages of early life. Freud was especially concerned about how these stages were related to sexual development in later life, and in this he was, and continues to be, quite controversial. In his time, it was considered by many to be outlandish that an infant sucking on her mother's breast was experiencing sexual gratification, yet Freud classified it as such and composed a theory of psychosexual development.
Freud's theory of psychosexual development suggests that children pass through several stages in their earliest years. These stages are the oral stage, the anal stage, the phallic stage, the latency stage, and genital stage. During each stage, children learn to gratify themselves (Freud would say sexually) via distinct patterns of behavior. During the oral stage, for instance, children learn that the highest level of physical gratification occurs through oral stimulation. (They feed by sucking, they routinely place objects in their mouths, etc.) It was Freud's view that during any one of these stages a person could become fixated—that is, they could be so gratified or, on the other hand, so unfulfilled, that they are marked for life by this fixation. Someone who has a fixation at the oral stage of development, for instance, might suck his or her thumb, eat or drink excessively, chew pencils, or smoke cigarettes. Adults fixated during this period of development are also thought to be inclined toward clinging, dependent relationships. Those fixated during the anal phase of psychosexual development are typically thought of as being overly controlling and obsessed with neatness or cleanliness.
Freud also considered regression closely linked to fixation. In his famous Introductory Lectures on Psycho-Analysis, he spoke of human development as a journey into new territory, much like an early migration of primitive peoples into new territory. He states that as people migrated into new, unexplored territory, certain members of the party might stop along the way at a place that offered them the prospect of a good life. These stopping points would be analogous to the fixations people develop in early life, attaching themselves to a period of safety and security before the entire journey of life is fully accomplished.
Freud, Sigmund. Introductory Lectures on Psycho-Analysis. New York: W.W. Norton & Co., 1966.