This kind of thing is called post-it notes ... as the name implies, it is convenient to stick on books and walls in places like home and office, and you can record some memos, mainly reminding (warning and encouragement). In junior high school and high school, I would buy post-it notes because I had to take a lot of notes in my textbooks ... Now there is this thing on the back wall of our class, which is exactly the same. The teacher said to write down the expectations and wishes of the university in recent years and go back after graduation in three years.