On the one hand, allowing a horrendous evil requires a much more potent justificatory reason. On the other hand, many horrendous evils do very obviously bring along with them the opportunities for very great goods–exercises of courage, compassion, patience, forgiveness, etc. Granted, many will query if the value of the opportunities would be sufficient to justify God’s allowing the horrendous evil, and intuitions will differ, but at least we can, typically, point to a number of uncontroversial goods of quite high magnitude. On the other hand, with the trivial evils it can often be harder to point to any goods (e.g., consider the uncomfortable pebble in one’s shoe).
So maybe it’s not harder to say in the case of the horrendous evil “There is a justification, but we don’t know what it is” than in the case of a trivial evil. But if so, then why is it that when we worry about the problem of evil, we are more apt to worry about greater evils than smaller ones?