Modern psychology conceives itself as the science of the human psyche. The psyche, in turn, is conceived as situated within each individual human subject. Hence the psyche is conceived as individual and internal. It is also associated intimately with the individual's brain inside the cranium. (The various occurrences of as in this piece stand for the hermeneutic As through which the world is interpreted from the ground up.) The pathology of the psyche, normally called mental illness, thus concerns the subject's individual psyche and is closely associated with malfunctions or defects of the brain. This opens the possibility for modern medicine to develop psychotropics that affect the individual's physical brain and, via this effect, affect the mentally ill patient's psychic state of mind for the better.
Even when the psyche's relationship with the individual's physical body is conceived in a more subtle, psychosomatic way, as in psychoanalysis, according to which, say, painful, repressed, unconscious memories of the patient find an expression nonetheless in physical symptoms, the psyche is still conceived as individual and as located somehow inside the patient, in the unconscious which itself is a part of encapsulated consciousness.
What if these conceptions of the human psyche are misconceptions that do not do justice to the phenomena of mind and psyche once a closer look is taken at the elementary phenomena themselves? What justifies treating the human psyche as individualized? What justifies locating the human psyche somehow inside the individual's body? What justifies relating the human psyche with the individual physical brain that even goes as far as treating the psyche as somehow efficiently caused by the brain's activity?
One main consequence of conceiving the psyche as individual is that psychopathology itself is individualized. If you're mentally ill, it's ultimately your individual problem. This holds even when psychological disturbances are conceived as resulting from the interaction of individual psyches, say, in a family 'system'. The psychotherapist's aim then is to uncover and improve interpsychic interaction among the system's members. The mentally ill individual needs to gain insight into what kind of games are being played with him or her that cause mental illness so as to regain mental health by changing the rules of psychic interplay.
But if the human psyche is individual and located somehow inside the subject, how could these individual psyches ever have anything to do with each other? That's easy, you say: They communicate with each other via language. But this move only shifts the problem: How is it possible that individuals share a language with each other through which they can communicate? To participate in any language, to learn it, the individual must be always already in the world with others from which he or she picks up the language. But picking up a language is an achievement of the individual's psyche, so it, too, must be always already in the world with others. It cannot be encapsulated inside an individual, especially not within an individual body.
Ah, you say, the individual is out there in the world via his or her physical senses which are receptive to what's happening in the world. According to current ways of thinking, however, the physical senses receive only physical sense impressions that are conveyed to the brain which interprets them as meaning this or that. How could it possibly be that such internal, individual interpretations of physical signals coincide? Through evolution, you say. How is that supposed to bridge the gulf between the individual psyche inside and the world outside? The world itself must be always already shared in some psychic way. And I don't mean the intellectually demented notion of telepathy.
What?! The psyche is always already out there in the world or even envelops the world!? And each individual human only ever partakes of this all-encompassing, shared psyche that must be conceived as openness for the world itself. This world is not merely the external, physical world taken in by the senses, but the world always already interpreted in various ways by the psyche by virtue of its originary openness that is open three-dimensionally to all that occurs at present, has occurred (memory) or will occur (expectation). Hence the world itself must not be taken as a given but conceived as taking place in the psyche, and not conversely, the psyche being conceived as taking in the world via sense perception.
Such a recasting of the psyche opens the vista on psychic disturbance that goes beyond a defective brain, the distorted perspective of a damaged individual's soul, the deformations of a dysfunctional social unit such as the family, to the hermeneutic blind spots in the psyche of an age.
In light of such an hermeneutic recasting, modern psychology would have some deep rethinking to do.
Further reading: A Question of Time, especially the chapters 'Out of your mind? Parmenides’ message' and 'Thinking in Clichés'.