All learning involves making errors. Knowing when errors occur and how to correct them is an important skill when developing the competencies needed to provide quality services as a clinical psychologist. From our clinical experience we have learned that a science-informed approach, while not perfect, is the best one available because, as Babbage said, the errors made are less than if we used no data at all. Good practice involves the integration of evidence-based treatment with treatment-based evidence, and is therefore inherently data-driven. Science can serve as an ally to the clinical psychology trainee by providing the foundation upon which the therapeutic relationship can flourish and produce beneficial outcomes. Although making errors when learning the complex tasks of a clinical psychologist may not be fun, the process of becoming a clinical psychologist deserves to be fun. The enjoyment comes from the excitement of developing new practical skills and gaining mastery in the effective delivery of therapeutic interventions. However, perhaps the most enjoyment of all comes from collaborating with another human being to bring about improvement in his or her well-being. Consequently, our aim in writing this book has been to provide a suitable companion on your journey to becoming a clinical psychologist. The journey and the destination should be enjoyable and, therefore, if we found it tedious to write about and irrelevant to the goal of becoming the best clinical psychologist, we left it out.