Only a few years ago one could observe, at least among German psychologists, a quite pessimistic mood. After the initial successes of experimental psychology in its early stages, it seemed to become clearer and clearer that it would remain impossible for experimental method to press on beyond the psychology of perception and memory to such vital problems as those with which psychoanalysis was concerned. Weighty 'philosophical' and 'methodological' considerations seemed to make such an undertaking a priori impossible.

p. v. - A Dynamic Theory of Personality, 1935