The document discusses various factors that can contribute to mental illness, including biological, cultural, and psychological factors. It divides life into stages from infancy to old age and discusses potential causes of abnormal behavior and challenges of adjustment at each stage. These include things like the quality of parenting and relationships in infancy and childhood, stresses of adolescence, crises of early adulthood, adjustments of middle age, and challenges of physical and social changes in old age. The document emphasizes that mental illness usually stems from multiple interacting factors rather than a single cause.