I have been pondering this question quite a bit...using Aristotelian/Thomistic categories. Is evil/suffering/pain/death etc. essential/substantial or accidental to this world and human experience?
I find the answer from a framework of naturalism must say "this is essential...fundamental to the way things are." Death, survival, reproduction...genes moving on through the cosmos perhaps hindered by our memes along the way.
Yet this seems to be strange because we seem to create a "problem of evil" - as if evil is a problem. and not a simple fact of the world. In a theistic worldview, evil is accidental, not essential and hence a "problem" - but this only makes sense if there is a good world...somehow gone bad with an alien invasion of suffering which is constant and objectionable by the creature.
So...essential or accidental? The answer to this question seems to set one's trajectory in life. Ask yourself a question - does your own suffering seem "right and normal" or really something "wrong."
Worth your time to think about...