[whatshisface]

Being anxious about a freight train heading straight towards you is not "anxiety" any more than grieving for the loss of a loved one is "depression." Medical doctors have absolutely nothing to do with the natural and accurate negative feelings associated with not being able to make rent.

[JacksonGariety]

But in most cases depression is a natural response to the difficulties of life. It's like when your immune system triggers an inflammatory response to infection. It's painful but natural; and the cause is external. Willpower can't cure depression any more than it can reduce inflammation. But in the case of mental illness, the external agent is socioeconomic hardship, family dysfunction, loss of a loved one, etc.