1 easy to remember, otherwise the book will be in a mess. How can others find books? Before, there was no search engine. With classification, people can have a systematic understanding of the structure of human science, and this function is irreplaceable even with search engines. There is a saying that people with different classifications in a library will never make scientific achievements again. Just like a book needs a table of contents, if you read a book from the first page to the last page, you can only say that you can't read it and you can't learn it. When reading a book, you should first understand the structure of a book, so that you can have a deeper understanding of the book.