When and why a colonoscopist should discontinue colonoscopy by himself?

Table 2 Kudo’s classification of colonoscopy difficulty

Difficulty classification	Presentation of correlative pattern
Grade A	Relatively short sigmoid colon, easy to be shortened. Applied to most young and middle-aged men. 2-3 min taken to reach the cecum
Grade B	Lengthy sigmoid colon and relatively tortuous descending sigmoid flexure, easier to form a loop
Grade C	Sigmoid colon with local or partial adhesion after abdominal disease, surgery, or unusually long sigmoid colon, with or without obvious tortuous descending sigmoid flexure, easier to form a loop