There are many problems, what is a "good life"? I think depression is just one of many problems. On the other hand, lets assume "good life" can happen to children, it can happen even if you are depressed, lets assume some intelligent children came and they understand their mother depression and help her. But that's all probabilistic stuff (good or bad) that one has absolutely no control over. But I won't talk here about the "inherent bads" in life and will just say that partial good/bad can be very probabilistic and gambling-like.
In my experience also, I think depression can be both inheritance and circumstances. Also, I think its something "triggered", so people imo are prone to depression and its not only genetic. If bad genetic and bad circumstances are mixed, then the probability will be higher (although some might still not be triggered). I don't know, its like a random function. I know why I got my depression (many stuff like childhood abuse and bullying then shifting places and many more then being fragile while having those depressing genes and many more stuff) but can't say about others, some people don't have any problem genetically or any circumstances but still get depressed, so its like a probability and none can be so sure about it.