What did Carl Rogers change by letting the client lead?

Carl Rogers changed who leads the session. In person-centered therapy, developed by Rogers and colleagues from the 1940s, the therapist does not tell the client what to do. Rogers believed that the answers to a client's questions were within the client and not the therapist, so the therapist's role was to create a facilitative, empathic environment where the client could discover them. He first called it non-directive therapy, and later client-centered.

What the therapist brings are three "core conditions": unconditional positive regard (accepting the client without judgment, disapproval or approval), congruence (genuineness, not "acting") and accurate empathic understanding. Rogers stated six necessary and sufficient conditions for change in 1957, and one of them is that the client perceives, at least a little, that the therapist's acceptance and understanding are there.

The history has a human thread. As a young intern in 1927 and 1928, Rogers studied with Alfred Adler. Used to what he later called the rather rigid Freudian approach of his institute, with seventy-five-page case histories and exhaustive tests before even thinking of "treating" a child, he was shocked by Adler's direct, deceptively simple way of relating straight away to the child and the parent. And in the 1940s, Rogers began calling his work "counselling" (Wikipedia credits him with coining the term) because psychologists in the US were not legally allowed to provide psychotherapy: only medical practitioners could use that term.

Wikipedia calls it the first theory of therapy driven by empirical research, and the first evidence was published in 1941, by Elias Porter, from recordings of Rogers's sessions. Wikipedia sums up the research as mixed but encouraging: generally positive for anxiety and depression, though some studies find it less effective than more structured approaches like cognitive behavioural therapy. Critics from the behaviourist side say it lacks structure, and critics from the psychoanalytic side call the supposed neutrality conditional.