In this article certain beliefs of mental health professionals were compared with the results of social and cognitive psychology. These beliefs refer to the trust in the value of clinical experience, intuition, relying on feedback from client/patient, trust in one's own objectivism or internal motivation of a patient to undergo therapy. Cognitive processes and errors in judgement, which lead to beliefs described in the article, usually have universal and unconscious character. They may, however, lead to incorrect assessment and treatment methods. These beliefs were assorted in such a way so as not to be connected with any particular therapeutical approach, but to characterize a certain way of thinking of the therapist about himself as an objective expert. Although the awareness itself of errors in cognitive mechanisms does not eliminate them from the work of mental health professionals, they can attempt to limit their influence through selfreflectivity and search for alternative explanations (to those previously assumed) in relation to what occurs during therapy. Conclusions emerging from studies of social and cognitive psychology concur with certain guidelines devised by postmodern mental health professionals.