According to the passage, what happens if the books are not changed?

Read the passage and answer the question. Many schools now use reading corners to encourage students to read every day. A reading corner is a small area in the classroom with books, cushions, and good lighting. Teachers say that students who spend fifteen minutes a day in the reading corner read more books and talk more confidently about stories. However, the books must be changed regularly, or students lose interest. According to the passage, what happens if the books are not changed?