Musar על ברכות 9:10

It is important for one who has trust in the Lord, Blessed be He, to know that the afflictions are for his own good, and in the end it will be well with him. As it is said, "Rejoice not against me, O mine enemy; though I am fallen, I shall arise; though I sit in darkness, the Lord is a light unto me" (Micah 7:8). And our Sages, of blessed memory, said, "If I had not fallen, I would not have arisen! And, if I had not sat in the darkness, I would not have seen the light!" (Shohar Tov 22:7). Therefore, any man who has troubles in his body, or with his money, or with his children, should set his heart to fast in addition to doing repentance, just as the community is obligated to fast in the time of their trouble, and as our Sages have decreed (Ta'anith 10a, 12b). Therefore, in time of trouble, a man should examine his deeds. If he has searched and has found no transgression, he should know that his afflictions have been prompted by God's love (Berakhoth 5a).