In his treatment of moral luck Adam Smith writes:
A man of humanity, who accidentally, and without the smallest degree of blamable negligence, has been the cause of the death of another man, feels himself piacular, though not guilty. During his whole life he considers this accident as one of the greatest misfortunes that could have befallen him. If the family of the slain is poor, and he himself in tolerable circumstances, he immediately takes them under his protection, and, without any other merit, thinks them entitled to every degree of favour and kindness. If they are in better circumstances, he endeavours by every submission, by every expression of sorrow, by rendering them every good office which he can devise or they accept of, to atone for what has happened, and to propitiate, as much as possible, their, perhaps natural, though no doubt most unjust resentment, for the great, though involuntary, offence which he has given them,”(Adam Smith, The Theory of Moral Sentiments, (TMS) 18.104.22.168; see also)
In context, Smith is relying on a distinction on being a voluntary and involuntary cause of harm. When we are voluntary causes we are subjects to judgments of propriety/impropriety and merit/demerit. When we harm others while being involuntary causes we're supposed to feel piacular (from "Latin piāculum propitiatory sacrifice, from piāre to appease")--a feeling that is markedly worse than agent regret, it is a species of shame that demands atonement (for the general mechanism in Smith, see here.)
The feeling of the piacular is an appropriate feeling. This is signaled by the fact that the man of "humanity" feels it. But if s/he is not guilty, why is this so? Sophie de Grouchy, a very fine philosopher who translated The Theory of Moral Sentiments, offers the following suggestion: "the sentiment is strong only because, being more connected to our memories, it is more present in us, and we have more trouble freeing ourselves from it." (Lettres sur la Sympathie, Letter V, p. 149 in this translation.) I doubt De Grouchy captures Smith's insight in this instance.
We like to think that if we are blameless then that is kind of the end of the matter in any moral situation; our deepest selves are untouched and we remain, as it were, pure. This is why when many students are introduced to the story of Oedipus (who, unsurprisingly is used as an exemplar of the piacular by Smith) and his family, they are inclined to say that "he didn't do anything wrong," or "he overreacted to his act of self-defense" (his clueless-ness, etc). By contrast, Smith is trying to capture a once-more-obvious, but now hard to grasp point: we are causes and it is part of our humanity to understand ourselves as such. This is as true of our (involuntary) victims as it is of ourselves. It is all-too-human to be instruments of fate. Smith rightly stresses we should not forget this otherwise inconvenient fact.
Some other time I discuss Smith's complex and very interesting treatment of the calculus in the moral commerce (which is sensitive not just to the gravity of the harm but also relative social status of victim and cause) that governs the proper atonement of this shameful feeling (in addition to the paragraph above, see also here.) But I end on an aspect of Smith's position that we children of the Enlightenment are most resistant to. From the point of view of rationality, the piacular can never be fully justified. (This is why sober folk prefer talk of "agent regret!") It is a proper, albeit superstitious feeling. This is why Smith introduces the language of the "piacular"--a Roman concept intertwined with bribery of the Gods. The moral economy that governs the piacular is one in which debts are discharged by virtue of sacrifice. This is fundamentally an instance of superstition as Smith explains in his Lectures on Jurisprudence. That is to say, according to Smith sometimes even our irrational reactive attitudes can be proper.