I have battled clinical depression for years. I consider myself one of the strongest people I know. Both "strong" and "weak" people can become depressed, just as can people of different races, genders, political parties, etc. Depression knows no boundaries. Yes, depression is related to the balance of molecules in our brain, which are in turn affected by outside events, our past, our thoughts, and our feelings. The mind-body connection. It's all interrelated. That's why both meds and psychotherapy can help depression.