Good Gosh! I never knew that. All I know is that he was a brilliant Viet strategos in the 11th century, leading a 100,000-strong Viet army on the offensive in an attack on China, and winning the encounter.
I don't really believe that any normally sexually inclined young man would voluntarily give himself in for castration, no matter how ambitious he might be. It would be just against his human-animal nature. What would have likely happened was that his poor parents offered him as a gift to the emperor, at a young age, for some monetary reward. The gift of a son or daughter would be considered the ultimate gift.
Then he becomes the absolute property of the emperor, to do as he pleases. Of course, the advantage of a eunuch warrior is that he's freed from the temptations of female flesh.
Additionally, the emperor then becomes the eunuch's sole raisson d'etre. His whole life, post castration, would be absolutely, totally defined by his service to the emperor. Nothing else matters.
Edited by Shield-of-Dardania - 29-Apr-2010 at 01:52