When and why a colonoscopist should discontinue colonoscopy by himself?

Table 1 Kudo’s colonoscopist level classification

Colonoscopist level	Presentation of correlative level
I	Mostly beginners, able to push forward the colonoscope body in the colon cavity; unable to use the method of the colon axis constriction to shorten the length of the colon
II	Able to push the colonoscope through the descending sigmoid flexure by α-loop or N-loop, and pull back the colonoscope to set free the loop when the colonoscope head reaches the transverse colon; then, use the method mentioned above
III	Able to control the colonoscope passing through the descending sigmoid flexure by α-loop or N-loop, and pull back the colonoscope to set free the loop when it reaches the descending colon; then, use the above-mentioned method
IV	Able to control the colonoscope and keep the colon axis constriction from rectosigmoid flexure, pushing the colonoscope passing through the descending sigmoid flexure without loop formation