For me it's a combo of nature and nurture. Bipolar and depression are in my family, and my diagnosis is Bipolar II. My first mood episode was a major depression at age 10 or 11. Then cycling through my teens, diagnosed with depression at 19, and bipolar not recognized until 29. In my childhood my parents divorced and my mom was depressed, then my sister was hospitalized for anorexia. So there was unhappiness around me that could have triggered it, but no specific event. When I was older there were hormonal triggers and stress that set off mood episodes. The worst was a depression and mixed episode following my divorce. I think my brain was vulnerable, and adverse events brought the depression out. My therapist just thinks I'm heartbroken, he thinks it's nurture, not nature.