Psychology is not only the study of human thinking, feeling, acting, and interacting: it has itself – like the other human sciences – brought into being new ways of thinking, feeling, acting, and interacting. We ordinary people whom the psychologist studies have turned out to be not quite the same ordinary people that we were before such extraordinary people as William James and Freud and Kohler and Piaget. Psychologists have had varying (sometimes striking) success in interpreting the human world; but they have been systematically successful in changing it.
Alasdair MacIntyre, “How Psychology Makes Itself True – or False”, in A Century of Psychology as Science, ed. Sigmund Koch and David Leary (New York: McGraw-Hill, 1985), 897, doi: 10.1037/10117-055.