There are many ways in which psychologists try to understand human behaviour - and the difficuty is that many of these approaches overlap. and this shows the complex nature and diversity of human behaviour. For example the scientific approaches, like behaviorism or cognitive psychology, tend to leave out the subjective (the personal) experiences that patients have. Another approach, the humanistic one, recognises human experiences, but is not very analytical or science-based in method and evidence presentation.
Psychodynamic approaches focus heavily on the patient's unconscious mind and on the importance of childhood experiences, particularly maternal care so it doesn't go far enough into the role of socialization (further complicated by cultural differences.) Biiological approaches are sometimes criticised for being too detached from humanity in that they only consider mechanisms or physical structures (heredity, predisposition, genetics) Obviously these are very important but consciousness and environment also influence behaviour profoundly.