《后汉书·列传·宦者列传》
宦官这种人，他们与普通人不同，名声不好，不是出身于贵族大家。肌肤血气不能传于后代，表面上看不出他的坏处，做事容易取得信任，加以在朝廷里见多识广，熟悉典章制度，所以年幼的君主，依靠他谨慎练达的长处，女君利用他出入听命方便。察访他没有猜疑忌惮的心思，接近他有可喜的颜色。
刑余之丑，理谢全生，声荣无辉于门阀，肌肤莫传于来体，推情未鉴其敝，即事易以取信，加渐染朝事，颇识典物，故少主凭谨旧之庸，女君资出内之命，顾访无猜惮之心，恩狎有可悦之色。
Eunuchs are different from ordinary people. They do not have a good reputation and are not from a noble family. The flesh and blood cannot be passed on to the descendants, and the appearance does not show his harm. It is easy to gain trust when doing things. Moreover, he has seen the world in the court and is familiar with the rules and regulations, so the young monarch relies on his prudent and knowledgeable strengths. The queen uses him to enter and leave orders conveniently. Visiting without suspicion or fear, being close to him has a sense of joy.