Musar על איכה 3:29

And the penitent is also obligated to be submissive and to fulfill and follow the path about which our Rabbis, may there memory be blessed, said (Avot 4:10), "Be of humble spirit before all men." And from this, he will acquire that he will not get angry at - or be exacting with - his fellows; and he will also not pay attention to everything that he hears and will forego his reckonings. And from this, all of his sins will be [forewent to be] atoned, as our Rabbis, may their memory be blessed, said (Rosh Hashanah 17a), "Whoever forgoes his reckonings [with others, the heavenly court, in turn,] forgoes all his sins" - measure for measure. And this is a very glorious opening for hope. And it is stated (Lamentations 3:29-30), "Let him put his mouth to the dust - there may yet be hope. Let him offer his cheek to the smiter; let him be surfeited with mockery."

But now consider that even in the quality of worry there is some good to be found, as the Prophet said, "Wherefore doth a living man complain — A strong man because of his sins?" (Lam. 3:29). The sinner should nurture sadness in his heart and grieve in the bitterness of his heart that he has rebelled against the Creator of all.