I do think it is helpful to identify the reasons someone is depressed in order to take a certain amount of the sting out of depression.
I had pretty severe depression a few years ago after losing someone close. I won't elaborate because I don't want to trigger bad feelings in anyone vulnerable, but I had very bad days. Once, on a good day, I promised myself that as bad as any pain got, I would never do anything to myself. It was like establishing a baseline for behavior. And those jagged feelings did soften over time and I'm very happy these days.
I was also in a relationship with someone for a few years who was diagnosed with severe clinical depression. He tried many things in terms of therapy and medication and the prognosis was always grim. He kind of had a turning point when we got away from medicalizing things and accepted that he was really effing depressed for damn good reasons. That is was a normal reaction and it was ok for him to feel how he did. And then he started to heal and now he doesn't suffer at all the way he used to.
In both instances, I noticed that having a healthy diet and decent rest and engaging in centering practices, like yoga and meditation, made a big difference. Even running and riding a bike helped. It may not cure things but it can make the bad days much less grim. Being more connected with nice people can really help too.