'Contemporary psychology has supplemented its traditional cabinet of curiosities, where inner substances such as 'intelligence' and 'extraversion' have long been on display, with the discovery of several others we didn't know we have. Virtuous substances such as 'self-esteem', 'grit', and 'self-compassion' are now exhibited alongside more noxious substances, such as post-traumatic stress disorder or Borderline Personality Disorder. For those who might, at this point, feel there are just too many inner substances to keep track of, Paul van Geert and Naomi de Ruiter offer some relief. They argue that many research programs in psychology get caught up in their own dubious assumptions, neglecting the vicissitudes of individual lives as lived over time. With learning and humor, ranging from Ancient Greece to Monty Python, they invite readers to contemplate a less rigid, more dynamic and process-oriented research agenda in psychology.' Paul Harris, Victor S. Thomas Professor of Education, Harvard University, USA