If you get stabbed in the eye twenty times with bamboo, you’re going to have a hard time beginning to calculate where anything is. Taking a bamboo shoot to the eye is no pleasant experience, especially if done twenty times. You’d be blinded for sure. And a newly blinded person is going to have one heck of a time calculating where everything is without the power of sight.
Do you know how Santa-san (さん) punishes naughty boys and girls in Asia? He doesn’t give them coal, Santa-san tortures them with twenty bamboo jabs to the eye. Yikes. Do you know how Santa-san calculates who is naughty and who is nice? By their school grades, of course.