The second suggestion has to do with the effect of exceptions. James says, "Never allow an exception to occur" in the course of forming a habit. Not only will the occurrence of one exception make more likely its recurrence, but if the exception does not recur, at least the response is less sure and less accurate than it otherwise would be. It tends to destroy self-confidence or confidence in the one who allowed the exception. Sometimes even one exception leads to disastrous consequences and undoes the work of weeks and months. This is especially true in breaking a bad habit or in forming a new one which has some instinctive response working against it. There has been a great deal of work done in experimental laboratories and elsewhere in the study of the formation of particular habits. The process of habit formation has been shown by learning curves. When these learning curves are compared, it becomes clear that they have certain characteristics in common. This is true whether the learning be directed to such habits as the acquisition of vocabularies in a foreign language or to skill in the use of a typewriter. Several of the most important characteristics follow. In the first place it is true of all learning that there is rapid improvement at first. During the beginning of the formation of a habit more rapid advance is made than at any other time. There are two principal reasons for this fact. The adjustments required at the beginning are comparatively simple and easily made and the particular learning is new and therefore is undertaken with zest and interest. After a time the work becomes more difficult, the novelty wears off, therefore the progress becomes less marked and the curve shows fluctuations.