In medical training you are accustomed to see things. You see an anatomical preparation, the precipitate of a chemical reaction, the shortening of a muscle as a result of the stimulation of its nerves. . . . In psycho-analysis, alas, everything is different. Nothing takes place in a psycho-analytic treatment but an interchange of words between the patient and the analyst. The patient talks, tells of his past experiences and his present impressions, complains, confesses to his wishes and his emotional impulses. The doctor listens, tries to direct the patient’s processes of thought, exhorts, forces his attention in certain directions, gives him explanations and observes the reactions of understanding or rejection which he in this way provokes in him.
Sigmund Freud, Introductory Lectures on Psychoanalysis, Lecture I.