It has struck many observers that the external provocation to quarrelling is often very trivial. Of course we frequently hear a man or his wife declare that they would gladly avoid a quarrel if it were possible to do so. Either one says something that seems to be quite innocent, and yet it will be the occasion for a heated altercation, a great domestic scene with all its unpleasant consequences. This is due to the fact that most persons do not distinguish between cause and provocation. The provocation to a quarrel is easily found if hidden unconscious forces seek for it, if a deeper cause, acting as a driving power, sets the wheels of passion in motion. A somewhat careful investigation of every quarrel easily brings the conviction that it is invariably the secret, unconscious emotions that bring about the conflict of opinions. Where this deep resonance of the unconscious is lacking we playfully pass over differences. Unfortunately there are probably no two human beings whose souls vibrate so harmoniously that there never occurs a discord. This phenomenon is altogether too deeply rooted in human nature for an exception ever to occur. And paradoxical as it may sound, it is lovers who love each other most who cause each other the greatest pain. The great intensity which their emotions attain is due only to the fact they have repressed a series of experiences and feelings. They are blind to the faults of the beloved because they do not wish to see these faults. But the suppressed forces have not yet lost their power over the soul. These bring about the quarrel, and are capable, even if only for a few seconds, to transform love into hatred. But a few practical examples will do more to make this subject clear than all our theoretical explanations. Mr. N. S., a pious, upright man, asserts that his present ailment dates from a quarrel that had been frightfully upsetting him for months. He had inherited from his father a large library rich in manuscripts, and had also succeeded him in his position. One day his brother came to him and stormily demanded the return of the books. But inasmuch as he was the older he felt himself entitled to be the sole heir. A violent quarrel ensued, during which he exclaimed: “I’ll die before I give up any of these books!” After the quarrel he became very neurotic. He tortures himself with self-reproaches; he is convinced that with that exclamation he had been guilty of an act of impiety; he is very unhappy and finds no rest, no peace, either at home or in his office. Many persons may be satisfied with the superficial explanation offered by the patient himself that he is an ardent bibliophile and collector of ancient manuscripts. But the physician who treats sick souls must not be so easily satisfied.