There are many curious obsessions that disturb people and that are often extremely difficult of explanation even by themselves. Dr. Johnson, one of the most sensible men in many ways in his time in England, could not, it is said, pass a post on the street without touching it. At least if he did so he felt that somehow he had omitted to do something that he ought to have done and it would make him uncomfortable. There are many people who have some idea that it is lucky to touch posts as they pass along and the number of people who do things like this is larger than might be imagined. Many people put themselves out of the way in order to avoid letting a post come between the person with whom they are walking and themselves because it is said to be unlucky. Most of them will laugh at it, but still they continue the practice in spite of the bother it may occasion them. Occasionally there is some incident in their past life which accounts for such obsessions, though the patients themselves are occasionally not quite conscious of them. Dr. Boris Sidis tells the story of a man who could not take a car with an odd number. Psycho-analysis showed that he had once seen a child run down by an odd-numbered car.

In such cases there has been a long series of suggestions that have created a dominant state of mind. The only way to overcome this when it becomes a serious annoyance is to undo the influence of the suggestions by a continued series of counter-suggestions, and by such discipline of mind as will prevent the former suggestion from exerting itself. The cure can be accomplished in this way, though, as a rule, the patient will need the help of someone else.