Yes, I know it's easy to be happy even in pitiable conditions. However I don't know if that the case for terminal conditions. I mean imagine someone who thought they had a perfect life only to be hit with the diagnosis of stage 4 cancer. 

This year my cousin's gave birth to a child even though she's had heart failure for over 3 years now, it was surprising she gave birth without and surgical produce. I wondered how, and it felt intriguing. This made me understand that the body is capable of far more than we know. 

You're right about depression being psychological, but most of the cases I know is a result of chronic issues that won't give a person some moment of relief. I've heard people commit suicide, it's saddening that sometimes people just wants to end it, rather than being part of this world.