What is an ugly book?
In fact, there is no unified concept of ugly books, and there is no such thing as ugly books in ancient times. It's a word made by netizens themselves, which is ugly-looking calligraphy.
This is very interesting. There is no fixed standard for being ugly. The same calligraphy, some people look ugly, and some people may look beautiful.
People who don't know calligraphy look beautiful, while those who know calligraphy feel ugly. How to define this? Obviously, this concept is not very rigorous, so there is a great controversy about ugly books.