The real sting here isn't that good people sometimes do bad things—it's that corruption requires a kind of blindness we mistake for virtue. Hemingway is suggesting that wickedness doesn't announce itself; it wears the mask of the naive, the righteous, the person who *knows* they're on the side of good. Consider how a parent might emotionally control a child under the guise of protection, or how a nation wages war convinced of its moral superiority—the harm begins not from malice but from an almost willful innocence about one's own capacity for harm. To read this carefully is to become suspicious of our own certainties.