IANAC. On this board I most often identify as theistic, but at some point it’s a choice of vocabulary and terminology, and you could deprive me of theistic terms and I could still communicate about it as an “atheist”.
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Suffering, like happiness, is rigged in us to be relative. No matter what the individual or social circumstances, the healthy human will generally find at least some joy, hope, satisfaction, and happiness in life; and will find at least some discontent, misery, thwarted fury, sadness, shame, loneliness, malaise, etc.
Emotions have a purpose, same as eyesight. We’re supposed to have feelings, and they don’t exist just like so many bonbons from Godiva Chocolates®, to smack our lips over the tasty ones and decry the existence of the ones we don’t like. They exist in order to give us motivation and direction. Human improvement, on an individual or a societal level, can be approached and attained by understanding the circumstances that maximize the good feelings, and/or mimimize the bad ones, and seeking to make those circumstances commonplace.
Emotions are the metaphorical fruit of the tree of the knowledge of good and evil. They are the apple, and it is right and proper that we eat of it, to know for ourselves what we should and should not be doing.
As things get better than they once were, the “zero settings” adjust accordingly, and things that perhaps didn’t bother us so much before become emotionally troubling to us.
That may not address what you meant to be asking, though. Are you (the OP) asking “why do bad things happen to good people” rather than “why do we experience things as bad”? (Saying it that way assumes that there are “bad things”, objectively speaking, and bypasses the “evaluation-as-good-or-bad” entirely). Some “bad things” happen for no particular reason (a random meteor flies out of the sky and smashes your kid before your eyes). Other “bad things” happen as a consequence of underlying situations that, after dwelilng on the misery the event brings, we decide we can do something about (a cruel martinet of the dictator’s security forces bashes in your kid’s head with a billy club before your eyes). Perhaps, though, even the things that seem “random” and beyond our ability to do anything about could be protected against if they were common, if we had the appropriate insight or technology, and/or if we had solved enough of the other shit that those were the ones that still existed to give us torment? (Maybe we’d build a meteor-tracking device to ensure that no more babies got killed by meteor strikes)