“The end of suffering does not justify the suffering, and so there is no end to suffering". (33)
This is a reocurring theme in the book that there is constant suffering and no release from it.
This comes up often in the book because Oskar has a lot of pain and suffering after the death of his father.
I believe Oskar makes himself suffer when he punches himself and makes bruises...it's a way of getting his anger and sadness out and it being real and noticable for himself to see, instead of it bottling up inside of him.