[Progress in psychology depends] upon keeping in mind that general validity of the law and concreteness of the individual case are not antitheses, and that reference to the totality of the concrete whole situation must take the place of reference to the largest possible historical collection of frequent repetitions. This means methodologically that the importance of a case, and its validity as proof, cannot be evaluated by the frequency of its occurrence. Finally, it means for psychology, as it did for physics, a transition from an abstract classificatory procedure to an essentially concrete constructive method.

p. 42 as cited in: Anthony C. Westerhof (1938) Representative psychologists. p. 48. - A Dynamic Theory of Personality, 1935