Durbin and Hicks were critical of standard cross-sectional research on relationships between personality and psychopathology. Operating from a view of traits and disorders as 'co-developing' phenomena, they called for increased use of longitudinal designs to characterize the interplay between the two, within individuals across time. They articulated specific principles surrounding this co-development perspective, discussed research directions and strategies that follow from these principles, and provided concrete empirical illustrations of the dynamic interplay between traits and clinical problems. We comment on specific ways this article stimulated our thinking. Copyright (C) 2014 European Association of Personality Psychology