The difference between obsessional personality (which can be an advantage in someone whose job involves routine attention to detail, such as an accountant or laboratory technician), obsessional personality disorder (which impairs spontaneity, social relationships, and task completion), and obsessional neurosis (in which thoughts, feelings, and compulsive behaviour patterns cannot be controlled by voluntary effort) is largely one of degree. While it is true that obsessional neurosis can develop in people who do not have obsessional personalities, it is, nevertheless, more likely to occur in people with this rather than any other type of personality. Moreover, there is no clear line of distinction between obsessional symptoms and normal experience. Compulsions, such as ‘having to’ avoid the cracks in the pavement, are extremely common in normal children, and most of us have, from time to time, experienced unwelcome thoughts, images, or tunes that come into the mind unbidden and will not immediately go away. People who seek psychiatric help for obsessional symptoms, however, generally do so only when they have become severely incapacitating.