Lately I've been reading about co-dependency. I'm impressed by how "naturally personalistic" so much of the literature around addiction and recovery is. It's put in plain terms, of course, but its practical wisdom very much embodies many of the deep philosophical principles formally worked out by great thinkers like John Paul II.
Here's one line (among dozens I might have chosen) from The New Co-Dependency, by Melody Beattie. "Suffering is how we feel about how we feel." In other words, it involves the kind of reflection and response that is only possible in a free and responsible subject, a self. Physical pain considered alone doesn't quite qualify.
This is why suffering is so deep a mystery. It makes sense of its incorporation into the mystery of redemption. Just reading that one line, I have a better grip on the relation between "freely-accepted suffering" and the overcoming-of-evil. It is, quite literally, the antithesis of death.