**Core Concept**
Diverticulitis is a gastrointestinal disorder characterized by inflammation of diverticula, small pouches in the wall of the colon. The condition can lead to various complications if left untreated or if treatment is delayed.

**Why the Correct Answer is Right**
Perforation of the diverticulum is a life-threatening complication of diverticulitis. When the diverticulum ruptures, it allows bacteria to spill into the abdominal cavity, leading to peritonitis, a severe infection of the abdominal lining. The perforation can also cause leakage of fecal material, further increasing the risk of infection.

**Why Each Wrong Option is Incorrect**
**Option A:** Bleeding from diverticulosis is a common symptom, but it is not typically associated with diverticulitis. Diverticulitis is an infectious process, whereas diverticulosis is a benign condition characterized by the presence of diverticula in the absence of inflammation.
**Option B:** Obstruction is a complication of other gastrointestinal conditions, such as cancer or Crohn's disease, but it is not typically associated with diverticulitis.
**Option C:** Fistula formation can occur in diverticulitis, but it is not as common as perforation.

**Clinical Pearl / High-Yield Fact**
Remember that diverticulitis is a surgical emergency if there is evidence of perforation or significant peritonitis. Prompt surgical intervention is essential to prevent further complications and improve outcomes.

**Correct Answer: C. Fistula formation can occur in diverticulitis, but it is not as common as perforation.**