Depression is not just a bad mood. This is one way to adapt to a reality that knocks the soil out from under your feet. The feeling of helplessness leads to the disconnection of all systems that are responsible for cheerfulness, and we can no longer experience pleasure. Richard O'Connor is a psychotherapist with 30 years of experience, detailing the causes of depression, its links to other diseases and offering a systematic approach to overcome it based on cognitive behavioural therapy.