LC, in my mind there is ONE reason for all sin and that is the desire to define Good and Evil for ourselves. That desire manifests itself in thousands of ways but the root cause remains in our corrupted DNA from great grandpa Adam to want to make our own way in life.
The application of that is to first recognize there will be no workable solution to your questions in this life. I think the best any of us can do is forget the big picture, we have absolutely no control of that, and try to make the world behind us a better place as we walk through.
I don't have a Phd, not even a BA. But I do have a DD214.
Common sense is an uncommon virtue