According to Jung, all psychic contents of which we are not yet conscious appear in projected form as the supposed properties of outer objects. Projection, from this point of view, is a displacement, occurring unintentionally and unconsciously, that is, without being noticed, of a subjective psychic content onto an outer object. In this process, the unconscious of the projector does not as a rule pick just any object at all but rather one that has some or even a great deal of the character of the projected property. Jung speaks of a "hook" in the object on which the projector hangs his projection like a coat.
— Marie-Louise von Franz
The hook matters more than we usually admit. It would be easier to say projection is pure error — that we simply paste interior contents onto the world and call them real — but Jung's image resists that comfort. The outer object is not neutral. It has something in it, some feature or quality that catches the unconscious like a notch in wood catches a nail. The projected content does not land randomly; it finds something to answer.
This is what makes projection so difficult to withdraw. You cannot simply say "that anger I see in him is mine" and be done with it, because he may genuinely carry anger — just not the specific, saturated, world-filling anger the projection required. The hook was real; the coat you hung on it was yours. Sorting those apart is the actual work, and it cannot be done by a decision to be more self-aware. It requires sitting long enough with the charged quality — the person, the place, the image that will not let you go — to discover what you need it to be carrying that belongs, instead, to you.
Von Franz is precise here in a way that protects the reader from a shallow interiority: the world still has properties. Projection does not make the outer unreal. It makes you a bad witness to it.
Marie-Louise von Franz·Psychotherapy·1993