It has often been observed that, in general, different psychotherapies do equally well. Some have taken this as good evidence that therapeutic action in psychotherapy rests not on the factors specific to individual therapies, but on common factors. I argue against this view in favor of a theory of therapeutic action deriving from psychodynamic psychotherapy. This identifies the therapeutic relationship (and with it, many so-called common factors) and “psychodynamic insight” as therapeutic factors. I review the evidence from outcome studies and from studies into two concepts related to insight, specifically reflection function and psychological defense. I argue that the best interpretation of the evidence supports the claim that insight, in interrelation with the therapeutic relationship, contributes to therapeutic action.