Two paradoxes of psychotherapy research — (a) various therapeutic approaches produce approximately equal outcomes despite wide differences in orientations, and (b) all psychotherapies generate clinical evidence that supports their theoretical positions—can be understood as instances of therapists systematically rewarding and extinguishing various client behaviors. Therapists’ belief in their theories serves as a self-fulfilling prophecy, both to produce change in clients and to confirm the theory. Evidence supplied by the client is, in part, a product of the interaction with a therapist. It is as mistaken to accept clinical evidence uncritically as it is to reject it out of hand. Experimental confirmation of clinical evidence is crucial.