During the reign of Zhu Yuanzhang, the founding emperor of the Ming Dynasty, in order to avoid repeating the mistake of eunuch's disorderly administration, it was stipulated that only people with low education could be recruited, because there were indeed literate eunuchs in politics and disorderly administration before the Ming Dynasty. Although this can make the emperor treat the eunuchs around him with snacks, in fact, in the late Ming Dynasty, there were still uneducated eunuchs like Wei Zhongxian who intervened in politics and made a mess of politics, which was unexpected by Zhu Yuanzhang.
During the reign of Zhu Yuanzhang, the requirements for eunuchs were strictly enforced, but in other periods of the Ming Dynasty, there seemed to be signs that eunuchs were no longer uneducated people. As far as Wang Zhen is concerned, he had achieved the status of scholar and juren before he entered the palace, and he also taught books. He should be regarded as a person with higher education. After all, it is not easy to get a juren in the Ming Dynasty. Later, he found it difficult to pass the exam and enter the official position, so he castrated himself and became a eunuch in the palace. It can be seen that the court was not required to recruit eunuchs during this period. Feng Bao, the great eunuch in Longwan period, was also a eunuch with high cultural accomplishment. According to historical records, during his tenure as the ceremony supervisor, Feng Bao had supervised the engraving of many books, such as Four Books, and was also proficient in music theory, and even had some attainments in calligraphy, which clearly reflected that Bao Feng had a certain cultural level.
Of course, in the Ming Dynasty, in addition to Wang Zhen being castrated as a eunuch for his own career, more people should be forced into the palace as eunuchs because of their livelihood. After all, there were still many people with food and clothing problems in ancient times, and most of these people were probably uneducated people. For example, Wei Zhongxian, a famous eunuch, was castrated into the palace to be a eunuch because he lost all his gambling. Wei Zhongxian was basically forced to make a living as an official.
In addition, the situation of the big eunuch Liu Jin is different. In his early years, he was adopted by a eunuch named Liu in the palace and castrated at an early age. Liu Jin was originally not surnamed Liu, but changed her surname to Liu because she was adopted by a eunuch named Liu. A eunuch like Liu Jin, in theory, won't have any culture. He won't understand whether he has taught himself or not.