Why do bad things happen to good people? Seneca's answer in On Providence is that nothing bad happens to a good person at all - what looks like misfortune is the material virtue is made from, and an untested character is simply an untested one.
The passages here cover pain, illness, exile, poverty and disaster, and they mostly share that shape: the event is not the problem, and the response to it is the only part that was ever going to be up to you.
36 passages
"Finally, in every event which leads you to sorrow, remember to use this principle: that this is not a misfortune, but that to bear it like a brave man is good fortune."
"Lay aside lamentations and wailings, and all the usual noisy manifestations of female sorrow: you have gained nothing by so many misfortunes, if you have not learned how to suffer."
"3 Just as she converts every obstacle and resistance, puts it into its place in the order of necessity and makes it a part of herself, so, too, the reasonable creature can make every obstacle material for himself and employ it for whatever kind of purpose he has set out upon."
"To the latter class belong good men in authority, good parents, teachers, and judges, whose punishments ought to be submitted to by us in the same spirit in which we undergo the surgeon's knife, abstinence from food, and such like things which hurt us for our benefit."
"I have done this by way of a heroic remedy: for I have determined to conquer this grief of yours, not merely to limit it; and I shall conquer it, I believe, if in the first place I can prove that I am not suffering enough to entitle me to be called unhappy, let alone to justify me in rendering my family unhappy: and, secondly, if I can deal with your case and prove that even your misfortune, which comes upon you entirely through me, is not a severe one."
"When some one tried to console our own countryman, Rutilius, for his exile, pointing out that civil war was at hand, and that all exiles would soon be restored to Rome, he answered with even greater spirit, "What harm have I done you, that you should wish that I may return to my country more unhappily than I quit it?"
"While tossed hither and thither by Catiline and Clodius, Pompeius and Crassus, by some open enemies and some doubtful friends, while he struggled with the struggling republic and kept it from going to ruin, when at last he was banished, being neither able to keep silence in prosperity nor to endure adversity with patience, how often must Marcus Cicero have cursed that consulship of his which he never ceased to praise, and which nevertheless deserved it?"
"But the harder these things are to bear, the more virtue you must summon to your aid, and the more bravely you must struggle as it were with an enemy whom you know well, and whom you have already often conquered."
"Remember, too, that many disagreeable feelings are identical with pain, and yet we do not perceive that they are; drowsiness, for example, and extreme heat, and loss of appetite."
"Nothing, therefore, nourishes anger more than excessive and dissatisfied luxury: the mind ought to be hardened by rough treatment, so as not to feel any blow that is not severe."
"When Caesar was besieging Corfinium, Domitius, who was shut up in the city, ordered a slave of his own, who was also a physician, to give him poison."
"When as they proceeded neither roots nor herbs were to be found in the sand, and they found a wilderness destitute even of animal life, they chose each tenth man by lot and made of him a meal which was more cruel than hunger."
"This you do not understand, and you bear a countenance which does not befit your condition, like many men who sit in the circus or the theatre without having learned that their home is already in mourning: but I, looking forward from a lofty standpoint, can see what storms are either threatening you, and will burst in torrents upon you somewhat later, or are close upon you and on the point of sweeping away all that you possess."
"Why? because he has made you capable of endurance? because he has made you magnanimous? because he has taken, from that which befalls you, the power of being evils? because it is in your power to be happy while you are suffering what you suffer; because he has opened the door to you, 1 when things do not please you?"
"Look around, I pray you, upon all mortals: everywhere there is ample and constant reason for weeping: one man is driven to daily labour by toilsome poverty, another is tormented by never-resting ambition, another fears the very riches that he once wished for, and suffers from the granting of his own prayer: one man is made wretched by loneliness, another by labour, another by the crowds which always besiege his antechamber."
"If an undirected welter, be glad that in so great a flood of waves you have yourself within you a directing mind; and, if the flood carry you away, let it carry away flesh, vital-spirit, the rest of you; for your mind it shall not carry away."
"Whenever you feel something hard to bear, you have forgotten ( a ) that all comes to pass according to the Nature of the Whole, ( b ) that the wrong is not your own but another's, further ( c ) that all that is coming to pass always did, always will, and does now everywhere thus come to pass, ( d ) the great kinship of man with all mankind, for the bond of kind is not blood nor the seed of life, but mind."
"It is like a fire, when it masters what falls into it, whereby a little taper would have been put out, but a bright fire very quickly appropriates and devours what is heaped upon it, and leaps up higher out of those very obstacles."
"If then it happens so that your nature can support it, do not complain but support it as it is your nature to do; but if so that your nature cannot support it, do not complain, for it will destroy you quickly."
""It would be better," say you, "if no one wished to do so." You are expressing a wish that the whole human race were inoffensive, which may hardly be; moreover, those who would gain by such wrongs not being done are those who would do them, not he who could not suffer from them even if they were done; nay, I know not whether wisdom is not best displayed by calmness in the midst of annoyances, just as the greatest proof of a general's strength in arms and men consists in his quietness and confidence in the midst of an enemy's country."
"If we accept with an undisturbed and tranquil mind that greatest terror of all, beyond which the angry laws and the most cruel masters have nothing to threaten us with, in which fortune's dominion is contained—if we know that death is not an evil, and therefore is not an injury either, we shall much more easily endure the other things, such as losses, pains, disgraces, changes of abode, bereavements, and partings, which do not overwhelm the wise man even if they all befall him at once, much less does he grieve at them when they assail him separately."
"As it is a consolation to a humble man in trouble that the greatest are subject to reverses of fortune, and a man weeps more calmly over his dead son in the corner of his hovel if he sees a piteous 10 funeral proceed out of the palace as well; so one bears injury or insult more calmly if one remembers that no power is so great as to be above the reach of harm."
"Seek out sufferings and all things hard to be borne, repulsive to be heard or seen; he will not be overwhelmed by their combination, and will bear all just as he bears each one of them."
"I did not even', he goes on, 'permit the medical men to give themselves airs as though they were doing some great thing, but my life passed on happily and brightly.' Do the same then as he did, in sickness if you are sick and in any other circumstance, for it is common to every school not to desert Philosophy in any at all of the accidents of life and not to gossip with the ignorant and unlearned."
The obvious risk in this doctrine is that it makes suffering sound useful, which is easier to write than to be on the receiving end of. It is worth reading Seneca here knowing he wrote from both ends - enormously rich, and also eight years exiled on Corsica.
Marcus offers the more portable version, and it concedes less: this is not a misfortune, but bearing it well is good fortune. That reframes without requiring you to believe the hardship was sent for your benefit.