In order to meditate properly, a monk must be able to eliminate all distractions. Each year the trainees will learn to ignore a specific stimulus, from loud noises, to cold, to pain. At the end of each year they are given a test; the masters will attempt to distract the students in whatever discipline they have been studying. For those learning to ignore sound, for instance, they will play large drums or cymbals, create explosions, and induce animal noises, all while the students maintain perfect composure. Or for sight, they will use brightly colored cloths, flashing lights, and even feign attacks on the students.
There is a strong incentive for the students to learn, for even the smallest reaction is cause for failure: a flinch, a sharp breath, a blink. The students are given only one chance before the option of failure is taken away forever. The crippled monks are not considered diminished in any way. They participate in monastery life up to the limits of their abilities. And there are even some things that only they are qualified for. Even among the masters it is rare to see any monk without scars.