In theory, it would that experimenter’s job would be least complicated if he could always work with the same subjects, thus coming to know their characteristics and controlling for their past experiences. While this often proves to be possible, there are some experiments which, by their very nature, can only be carried out once on a given subject. For example, in his studies of double alternation behavior, Hunter found that once the human subject came upon the solution to the problem, the experiment was over and the subject could not be used again.