The teacher said to the students, “You need to work hard if you want to pass the test.”

The teacher emphasized to the students that they must put in effort if they are to succeed in the test. One of the most significant discoveries of the early 20th century was the unconscious. It was appreciated that what we know of ourselves in ordinary consciousness comprises only a fraction of what is actually at play within us, and that a lot of what we really want, feel, and are is not at our mental fingertips, lying instead in a penumbra of ignorance, fantasy, and denial which we can only hope to dispel with patient and compassionate efforts, probably with the assistance of an analyst. Sigmund Freud’s The Interpretation of Dreams (first published in Vienna in 1900) was the landmark study of the workings of this unconscious region, and detailed the mind’s relentless attempts to hide a great many of its most salient truths from itself in the form of dreams which might shock, disturb, or excite us while they unfolded, but would then be deliberately forgotten or misunderstood upon our waking.

At much the same time, 700 kilometers to the west, over the border in Switzerland, another pioneering figure in early psychoanalysis, Carl Jung, took a complimentary but more direct and arguably more robust approach. Still only in his late 20s, Jung held a prominent position in Zurich’s former psychiatric institution, the Burghölzli Clinic, and understood that many of his patients were suffering from symptoms created by a conflict between what they deep down knew of themselves and what their conscious minds could bear to take on board about their feelings and desires.

Someone might, for example, lose all ability to speak because of one or two things they so longed but were so afraid of communicating to particular people. Another might develop a terror of urinating because of a humiliation that they had suffered in childhood, but that they lacked the wherewithal to remember and process.

Following Freud, Jung believed that healing and growth required that we learn to untangle our mental knots and more fully appreciate our complicated, sometimes surprising yet real identities. Freud had concentrated on interpreting his patients’ nighttime visions and in listening to them speaking at length in unhampered ways on his therapeutic couch. Jung felt that this took far too much time and was too much at the mercy of the right chemistry between analyst and patient. So, together with his colleague Franz Ricklin, in 1904 he developed what he took to be a more reliable technique, which he termed the word association test.

In this test, doctor and patient were to sit facing one another and the doctor would read out a list of 100 words. On hearing each of these, the patient was to say the very first thing that came into their head. It was vital for the success of the test that the patient tried never to delay speaking and that they strive to be extremely honest in reporting what they were thinking, however embarrassing, strange, or random that might seem.

Jung and his colleague quickly realized that they had hit upon an extremely simple yet highly effective method for revealing parts of the mind that were normally relegated to the unconscious. Patients who, in ordinary conversation, would make no allusions to certain topics or concerns, would in a word association session quickly let slip critical aspects of their true selves. Jung grew especially interested in how long his patients paused after certain word prompts. Despite the request that they answer quickly in relation to certain words, patients tended to grow tongue-tied, unable to find anything they could say, and then protesting that the test was silly or cruel. Jung did not see this as coincidental; it was precisely where there were the longest silences that the deepest conflicts and neuroses lay. A literal tussle could be observed between an unconscious that urgently wanted to say something and a conscious overseer that equally urgently wanted to stay very quiet indeed. In a given test, the doctor might say angry' and the patient might respond mother’; they would say `box’ and the patient might respond…