Just wanted to say depression is my main area of study, and especially the beginning of this post is kind of an extreme oversimplification/bordering on false statements about depression.

Stress actually plays a HUGE role in one's susceptibility, in combination with genes. This model of depression is referred to as the diathesis-stress model (genes would be the diathesis in this case). My lab studies the impacts of early life stress on the development of depression later in life, and we know that people with significant stress in their lives are much more likely to develop depression regardless of their genetic makeup. Life stressors could include things like being abused, having a parent die at a young age, and growing up in poverty.

Additionally, while we suspect there is a genetic component to depression and a lot of research supports that, NO ONE has actually been able to confirm the existence of "depression genes". For a while scientists thought the 5-HTTPLR gene which is a serotonin transporter gene was maybe an important gene in depression, but we realized it is actually just one piece of a much larger puzzle and not necessarily indicative of susceptibility to depression.

Combining these two points, a lot of research lately has been done on the HPA Axis which essentially regulates stress and negative emotional response, and we are finding that depressed people have malfunctioning feedback loops within this circuit. We don't know yet whether they had those before, or those were developed as a result of the depression. But this mechanism is the source of "rumination", which you kind of touch on with positive attitude, where a person has a negative thought and just keeps circling back to it and digging themselves into a hole. This isn't a choice they are making, this is a malfunction of signaling in the HPA Axis between the sACC and I believe the DLPFC (Dorsolateral prefrontal cortex).

But anyway, this has been a long drawn out comment, but I wanted to make sure everyone knew that while there are certainly things you can do to help prevent depression, honestly a lot of the prevention needs to come externally. For example, parenting styles impact a child's risk of depression. Teaching people how to regulate their feelings and recognize negative feedback loops helps people gain resiliency, but it's often something that can't be done alone and requires outside assistance. If you do get depressed, that doesn't mean you did anything wrong. Just because you are a lifelong vegan and you go on a ten mile run every morning does not mean you can't or won't develop crippling depression. I have lots of thoughts on this post, but I'll leave it at that.