We therefore tell him that the success of the psycho-analysis depends on his noticing and reporting whatever comes into his head and not being misled, for instance, into suppressing an idea because it strikes him as unimportant or irrelevant or because it seems to him meaningless. He must adopt a completely impartial attitude to what occurs to him, since it is precisely his critical attitude which is responsible for his being unable, in the ordinary course of things, to achieve the desired unravelling of his dream or obsessional idea or whatever it may be. (2.1.8)
For Freud, psychological repression goes hand-in-hand with its cousin, self-censorship. In Freud's view, as we mature, we learn to suppress, censor, and dismiss many of the thoughts and ideas that occur to us throughout our waking and dreaming lives—basically because we think those thoughts and ideas are silly, nonsensical, inappropriate, disturbing, or even truly horrifying. Freud argues that by recognizing and coming to terms with even the most disturbing of our thoughts and ideas, we can all have healthier mental lives.
Chapter 5, Section D
King Oedipus, who slew his father Laïus and married his mother Jocasta, merely shows us the fulfilment of our own childhood wishes. But, more fortunate than he, we have meanwhile succeeded, in so far as we have not become psycho-neurotics, in detaching our sexual impulses from our mother and in forgetting our jealousy of our fathers. Here is one in whom the primaeval wishes of our childhood have been fulfilled, and we shrink back from him with the whole force of the repression by which those wishes have since that time been held down within us. (5.5.46)
Throughout The Interpretation of Dreams, Freud argues that we repress whatever ideas, desires, and experiences are most disturbing to us—in other words, whatever impressions seem to threaten our safety or sense of self.
Chapter 7, Section D
Let us assume, then, that the suppression of the Ucs. is necessary above all because, if the course of ideas in the Ucs. were left to itself, it would generate an affect which was originally of a pleasurable nature, but became unpleasurable after the process of "repression" occurred. (7.5.15)
In Freud's view, as we mature, we learn to recognize that some of the wishes and ideas that we entertained as children are socially unacceptable for adults. Many of these wishes and ideas are sexual, but they also include things like extreme selfishness, greed, jealousy, hatred, and hostility. Freud says that because our adult selves have learned to view such wishes and ideas with displeasure, their expression results in "unpleasure," anxiety, and distress.
Chapter 7, Section E
This effortless and regular avoidance by the psychical process of the memory of anything that had once been distressing affords us the prototype and first example of psychical repression. It is a familiar fact that much of this avoidance of what is distressing—this ostrich policy—is still to be seen in the normal mental life of adults. (7.6.32)
Although Freud uses a number of spatial metaphors throughout The Interpretation of Dreams that suggest that unconscious or repressed thoughts are "buried" or "below the surface" of our conscious minds, the term "avoidance" gets closer to the heart of his theory. In Freud's view, repressed thoughts are not literally being "pushed down" into some bottomless pit in our unconscious; they're simply being ignored.
If we restrict ourselves to the minimum of new knowledge which has been established with certainty, we can still say this of dreams: they have proved that what is suppressed continues to exist in normal people as well as abnormal, and remains capable of psychical functioning. (7.6.41)
Throughout The Interpretation of Dreams, Freud stresses that the psychical processes he describes don't just occur in the minds of neurotics and "hysterics"—they apply to everyone. Freud's theories asked respectable ladies and gentlemen to radically re-conceptualize their own relationships to sexuality, society, and their deepest selves.
But this much is a fact: the primary processes are present in the mental apparatus from the first, while it is only during the course of life that the secondary processes unfold, and come to inhibit and overlay the primary ones; it may even be that their complete domination is not attained until the prime of life. (7.6.37)
As editor James Strachey notes, Freud associated the "primary processes" with the unconscious, and with "free" or "mobile" psychical energies, while the "secondary processes" are associated with the preconscious, and with "bound" or "quiescent" psychical energies (7.6.34). In Freud's view, repression is the result of a fundamental conflict between primary and secondary thinking.
On the contrary, the unpleasure principle takes control and causes the Pcs. to turn away from the transference thoughts. They are left to themselves—"repressed"—and thus it is that the presence of a store of infantile memories, which has from the first been held back from the Pcs., becomes a sine qua non of repression. (7.6.38)
Popular knowledge of Freud's theories tends to represent repression as a kind of "pushing down" of ideas that are upsetting, distressing, or uncomfortable. How often have you heard people say that they'd like to "repress" a thought or image that grosses them out? But here in The Interpretation of Dreams, Freud doesn't suggest that repression is an active act of "pushing down." Instead, it's a process in which certain thoughts are simply "left to themselves."
The memories on the basis of which the unconscious wish brings about the release of affect were never accessible to the Pcs., and consequently the release of the affect attaching to those memories cannot be inhibited either. (7.6.38)
In Freud's view, the "preconscious" (Pcs.) is always going to do its best to inhibit the expression of wishes that will result in unpleasure, anxiety, or distress. But because unconscious memories are inaccessible to the preconscious, all it can do is try to censor them as best it can. That's why dream-thoughts are subject to so much distortion.
Let us bear this firmly in mind, for it is the key to the whole theory of repression: the second system can only cathect an idea if it is in a position to inhibit any development of unpleasure that may proceed from it. (7.6.33)
"Cathexis" is one of those totally Freudian terms (well, Freudian in translation) that needs a bit of extra explanation. The simplest way to think of it is as a kind of psychical "attachment," or as the investment of psychical energy into an idea.
Among these wishful impulses derived from infancy, which can neither be destroyed nor inhibited, there are some whose fulfilment would be a contradiction of the purposive ideas of secondary thinking. The fulfilment of these wishes would no longer generate an affect of pleasure but of unpleasure; and it is precisely this transformation of affect which constitutes the essence of what we term "repression." (6.1.11)
In Freud's view, as we mature and are socialized, we learn to think of certain wishes, desires, and impulses as being distasteful—particularly those related to sexual taboos or those that emerge from excessive forms of anger, jealousy, or greed. Because our adult selves would find it distressing to see these infantile wishes realized—as in cases where adult dreamers dream of the deaths of loved ones—these wishes are repressed.