He seemed slow. But I knew he did not come to his somber garb by any tardiness of action or hesitancy in deed. The training of the assassin is thorough and cruel. He who wears the black of that caste has not won it easily. Candidates for the caste are chosen with great care, and only one in ten, it is said, completes the course of instruction to the satisfaction of the caste masters. It is assumed that failed candidates are slain, if not in the training, for secrets they may have learned. Withdrawal from the caste is not permitted.
Training proceeds in pairs, each pair against others.

Friendship is encouraged. Then, in the final training, each member of the pair must hunt the other. When one has killed one’s friend one is then likely to better understand the meaning of the black. When one has killed one’s friend one is then unlikely to find mercy in his heart for another.
One is then alone, with gold and steel.

Beasts of Gor ~ Page 358