In this article the idea of a transtheoretical metamodel is developed, which is especially focused on change processes in severe mental illnesses such as personality disorders. Mental flexibility is defined as a core process of change that can be promoted through implicit learning. Certain attitudes and techniques derived from mentalization-based therapy (MBT) and the learning components developed in the parent-child program Mediational Intervention for Sensitizing Caregivers (MISC) are recommended. The goal of the therapy is to open the epistemic learning highway and exercise the muscles of reflective thinking (mentalizing) during sessions to ultimately improve cognitive flexibility outside the therapy room. The change process towards mental flexibility replaces the idea of a corrective emotional experience because it has been shown to be less effective or even harmful, at least for the treatment of personality disorders. The integration of MBT and MISC also creates the possibility of training and observing behaviorally anchored, and therefore observable actions of therapists at a granular level. This opens up the possibility of observing and controlling microprocesses. It is therefore proposed to focus attention and understanding on implicit learning within therapeutic relationships, i.e., the internalization of a new way of thinking in relation to specific life events that require adaptation. Mental flexibility gives rise to flexible adaptive skills that make patients autonomous and should therefore be further investigated in future process research.