Initially, the idea of introducing Experience Sampling in psychiatric research aimed at incorporating ethnographically and ecologically relevant variables into clinical care. More provocatively, we sought to challenge psychiatric thinking with a new data set anchored more solidly in the experience of the person. We wanted to investigate if variables such as daily time-budgets, variations in mental state, situational reactivity and temporal patterning of symptoms would better describe and predict course and outcome. We wished to manufacture more valid psychiatric diagnostic profiles that would be able to specify treatment requirements more concretely. Quantitative descriptions of daily life patterns of ill and normal individuals would provide these data. Theoretically, the day and its behavioral components would open the window from which the history of the person, and the dynamics of his relationships, could be viewed. We wished to place the person more central than he currently stands in diagnostic formulations by emphasizing individual variation in experience and treatment tailored to individual needs. We thought that by confronting directly the often-ignored reality of individual differences, a powerful and persuasive argument for expanding the scope of treatment strategies could be made, ultimately resulting in a better fit between the person and the medical system.