Diverticulosis happens when the lining of the colon pokes through the muscles on the outside of the colon, causing pockets that look like indentations. And while diverticulosis is common, it’s mostly inconsequential and asymptomatic. Diverticulitis, however, is a different animal. That’s where one or a couple of the pockets get inflamed, and it can result in pain in the lower abdomen, constipation, or diarrhea.