Why is there a plastic stick on the cover of the book?

Used to fix the cover of a book. The book cover is a cardboard box with an opening on one side, which is slightly larger than the book to be placed. Feel good, easy to stick, the reference line is not dense enough, fancy is useless, the viscosity needs to be strengthened, and the spine is easy to degum. A plastic stick was given to fix the cover of the book. When placing a book, push the book out of the opening of the book cover and make the spine of the book outward so as to make it easier to see the title.