Many years ago I was in excruciating pain and I passed a tiny tiny piece of grit. I had seen kidney stones before (sister's souvenir) and when I saw how tiny my piece of grit was, and knew how much pain it caused me, I was amazed at what other's must go thru with real sized stones trying to pass thru narrow narrow tubes.
From google:
In human anatomy, the ureters are tubes made of smooth muscle fibers that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually 25–30 cm (10–12 in) long and around 3–4 mm (0.12–0.16 in) in diameter.